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The Garmin Fenix 5X is the top of the range of Garmin's running/outdoor watches. It has an impressive array of features, and it uses high quality materials to achieve a high-end look. It's only real weakness is its rather mediocre GPS accuracy, though this can be easily remediated by combining it with the [[Stryd]]. Of course, all this comes at a fairly hefty price, as the Fenix 5X retails for $700 (plus $200 for the Stryd.) '''Note: I'm still writing this review, so please consider it early access to my initial testing resultsve seen credible reports that the Fenix 5 and 5S models (but not the 5X or 935) have problems with their sensor support and I'd recommend avoiding those models until the issue is resolved.''' =Support This Site=The Fenix 5X is also available as the [[Garmin Fenix 5X Plus]].

There are four versions of the Fenix 5, one of which is branded as the Forerunner [[Garmin 935]]. (The You can think of the 935 is a plastic bodied Fenix 5 for $100 less.){| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"

! Forerunner [[Garmin 935]]

| <jfs id="B01MQX3306" nonl="true" n="Fenix 5X"/>| <jfs id="B01N7J9APR" nonl="true" n="Fenix 5"/>| <jfs id="B01NBL9XGP" nonl="true" n="Fenix 5S"/>| <jfs id="B01N7J9APRB06XGD6CS4" nonl="true" n="935"/>

Within each model, there are choices of wristband type, with a metal wristband adding $150 and sapphire glass adding $100. There are also a number of color choices, though the 5X is only available in gray. So, which to buy? I'd recommend getting the [[Garmin 935 ]] as it's cheapest. The only reasons to buy the Fenix version are if you need the full color maps (5X), WiFi (any with Sapphire glass), you want the Fenix look, or you want the smaller size of the 5S5X. Of course, with the release of the Fenix 5, you can get the [[Garmin Fenix 3 ]] at a lower cost. The [[Garmin Epix ]] is also worth considering as it has the maps of the 5X, but Garmin has stopped releasing firmware updates and itmost of the other functionality. '''s nowhere near <br/>There are credible reports that the smaller Fenix 5 and 5S models are having issues with sensor support. The reports suggest that Ant+ connectivity is poor, as well as attractivesome suggestions that the Bluetooth range is more limited than it should be. (These problems do not seem to be in the related "plus" models, the Fenix 5+ or 5S+.)'''

As noted above, while the Fenix 5X has poor GPS accuracy, even the best GPS watch is still not good enough for accurate pacing. The answer currently lies with [[Stryd]] and extremely accurate Footpod that can measure distance and pace far better than GPS. The Fenix 5X has the best level of Stryd support, and will allow you to have all the accuracy of Stryd for pace and distance while having GPS active. This allows you to maintain all of the navigation features of the Fenix 5X, as well as recording a GPS track for later use. You can even get an estimate of your [[Running Power Meters| Running Power]] from Stryd via a [[Connect IQ]] data field. I'd strongly recommend getting a [[Stryd]] Footpod to go with your Fenix 5X. If that's too expensive, I'd argue that you're much better off getting the Stryd and saving money by getting a cheaper watch like the [[Garmin Fenix 3]]. For a walkthrough on adding Stryd, see the section at towards the end of this article.

The Fenix 5X is a big watch, and it's larger than I'm comfortable with as a 24 hour/day activity tracker. However, on the run it fells okay even on my diminutive wrists. The watch straps rotate where they connect to the watch body, unlike the Polar V800 where they extend from the watch body and therefore don't conform as well. The materials are excellent quality, and while it doesn't have the simplistic elegance of the [[Suunto Spartan Ultra]] it's still very nice. The exposed bolt heads make the Fenix 5 look rugged and sporty, though it's a bit fussy visually. The only thing that feels a little cheap and tacky is the watch strap itself on the cheapest version. It's nothing like the silky smooth and soft watch material that Suunto use(Garmin watch straps always seem poor to me.) I find the weight of the Fenix 5X to be quite intrusive at times. I suspect it's the combination of the size and weight, as the thickness of the watch puts some of the weight further away from your body. When I swap between the Fenix 5X and the 935, the weight difference is quite dramatic. The display is reasonable, but when you compare it to the [[Suunto Spartan Ultra]] it seems a little small and low resolution. Given that the Fenix 5X is larger than the Fenix 5, I would've expected a larger display, but that's not the case. I suspect that the Fenix 5X is larger to allow for more memory for the maps, or perhaps more battery, though this is purely speculation.{| class="wikitable" style<gallery widths="margin-left: auto; margin-right: auto; border: none;"|- valign200px heights="top"200px>|[[File:Fenix 5X Tiny Wrists.jpg|none|thumb|x300px|The Fenix 5X is rather large on my small wrists. ]]|[[File:F3-F5X-Epix.jpg|none|thumb|x300px|Left to right, [[Garmin Fenix 3]], Fenix 5X, [[Garmin Epix]], all having some of the best [[Stryd]] support.]]|- valign="top"|[[File:V800-F5X-SSU-920XT-Above.jpg|none|thumb|x300px|Left to right, [[Garmin 920XT]], [[Suunto Spartan Ultra]], Fenix 5X, [[Polar V800]], seen from above.]]|[[File:V800-F5X-SSU-920XT.jpg|none|thumb|x300px| Left to right, [[Polar V800]], Fenix 5X, [[Suunto Spartan Ultra]], [[Garmin 920XT]], all rather large watches.]]|- valign="top"|[[File:Fenix 5X F3 SSU Dark.jpg|none|thumb|x300px| Left to right, [[Suunto Spartan Ultra]], [[Garmin Fenix 3]], Fenix 5X.]]|[[File:Fenix 5X F3 SSU Side.jpg|none|thumb|x300px| Left to right, Fenix 5X, [[Garmin Fenix 3]], [[Suunto Spartan Ultra]].]]|}</gallery>

[[:File:Fenix 5X and 920XT Buttons.jpg|center|thumb|300px|]]

{| class<gallery widths="wikitable" style200px heights="margin-left: auto; margin-right: auto; border: none;"|- valign="top"200px>|[[File:Fenix 5X Map UI (1).jpg|none|thumb|200px|This is the map display.]]|[[File:Fenix 5X Map UI (2).jpg|none|thumb|200px|A long press on the up button brings up this menu.]]|[[File:Fenix 5X Map UI (3).jpg|none|thumb|200px|The pan/zoom first uses the up/down to zoom.]]|- valign="top"|[[File:Fenix 5X Map UI (4).jpg|none|thumb|200px|Hit enter and you move to the pan up/down.]]|[[File:Fenix 5X Map UI (5).jpg|none|thumb|200px|Enter again to pan left right. ]]|[[File:Fenix 5X Map UI (6).jpg|none|thumb|200px|Enter again moves back to zoom, or back goes to the map display.]]|}</gallery>

Most of the configuration of the Fenix 5X is done directly in the watch, but there are aspects that have to be done via either the website, the smart phone app, or the PC (Garmin Express.) The main thing that you can't do on the watch itself is configure Connect IQ apps, watch faces, and data fields. The configuration on the watch is fairly intuitive, but the sheer number of configuration options can be a little bewildering, and if you have to do a factory reset, you have to apply all configuration changes again from scratch. While that's a bit of a pain, it's rarely a problem in practice, and more than made up for bite by the ability to configure the data shown during a workout without needing an Internet connection. Even better, you can configure the data shown during the workout actually during the workout itself. I find that surprisingly useful; just today it turned a little warm, and I was able to reconfigure my display to show the current temperature. It's not obvious (or it wasn't obvious to me) but you can copy a sports mode so that you can have multiple configurations for different types of work out. That way you can have a run based work out for easy runs, long runs, into full training, etc. this is rather nice, especially with the [[Stryd]] Footpod providing accurate pace information, which makes the pace alerts especially valuable. There is a limit that only allows two Connect IQ data fields, so having multiple workout types are allows you to have different combinations for different types of training.=Connect IQ=''Main article: [[Connect IQ]]'' Garmin's Connect IQ allows for the creation of apps to run on Garmin's running watches in much the same way you can run apps on Android or and iPhone. I've found the Connect IQ apps to be really valuable, and we're starting to see the number of apps explode, and the quality of the best apps has become remarkable. Many of the third-party apps are better than the Garmin developed apps, and significantly better than the built-in functionality. Below are two of my favorite watch faces, "ActiFace" and "GearMin" along with two of my favorite data fields "Single Field" and "Flexirunner". <gallery widths=200px heights=200px>File:Actiface 2.png|This is "ActiFace", my favorite watch face for a long time, with a nice graph of steps over the last week, plus lots of other data.]]File:GearMin 2.png|A rival to ActiFace is the "GearMin" watch face that improves on some aspects. I tend to swap between the two, and haven't found a clear winner yet.]]File:Single Field 1.png| I find myself using "Single Field" more often than any other. It puts a lot of data on the screen in a nice, usable fashion. There is a lot of customization with this data field, and the display uses color to show heart rate and cadence out of range. Search for "Single Field" by "lcj2" to find it.]]File:Flexirunner 920.png|There's even more data on Flexirunner by IMGrant.]]</gallery>As a tangent, Garmin gives us this heart rate graph widget, which color codes zone, shows heart rate, along with the minimum and maximum in the time window, so why can't we have something similar built in to the activity data screens? [[File:Fenix 5X 02.png|center|thumb|200px|]]=Activity Tracking=The Fenix 5X has a similar activity tracking support to most of the rest of the range of recent Garmin watches. The biggest problem I find with the Fenix 5X is an activity tracker is simply its physical size and weight, and I'd much rather have a smaller watch for wearing 24 hours a day. You can get a lot of the activity tracker functionality on a much smaller device such as the [[Garmin Vivoactive]] or [[Garmin Vivoactive HR]]. The Fenix 5X will track various aspects of your daily activity:* '''Workouts'''. Obviously, the Fenix 5X will track your runs, and will integrate that information into an overall picture of your daily activity levels. * '''Steps'''. The step counting in the Fenix 5X is comparable to other devices. When you're walking or running its pretty accurate, but there are other situations where it's a genuinely ambiguous as to whether you are taking steps or not, such as preparing food in the kitchen. I found that the Fenix 5X recorded a very similar number of daily steps as other Garmin devices I wore on the other wrist, which gives me some confidence in their consistency at least.* '''Floors Climbed'''. The Fenix 5X, along with a number of other recent Garmin watches, use the barometric altimeter to determine when you're going up or down steps. This is a rather nice idea, but the accuracy seems to be rather poor. I find the Fenix 5X will report a different number of steps ascended to descended, even though I've never used an elevator on those days. There's also a significant discrepancy between Garmin watches worn concurrently.* '''Intensity minutes'''. It's not clear how Garmin calculates "intensity minutes", but it seems to use heart rate to determine intensity, with high levels of intensity counting as a multiplier on the actual number of minutes. I've seen some strange discrepancy in intensity minutes when using the optical heart rate monitor, which is not surprising given the accuracy issues. I suspect that changes in the heart rate zone also impact intensity minutes, but the lack of transparency in this calculation makes it hard to evaluate.* '''Sleep'''. The estimation of sleep can be a little flaky on occasions, but overall it seems to do a reasonable job. It's hard to verify the estimation of sleep, other than checking if the bedtime and rising time seem reasonable. I'm not convinced by the Garmin estimate of how much deep and light sleep you are getting, and I tend to ignore that information as suspect. I have noticed that changing time zone can really mess up the sleep calculation, but hopefully Garmin will resolve this at some point.* '''Resting Heart Rate'''. It uses two methods of detecting resting heart rate. If you wear the watch overnight with the OHRM enabled, it will be the lowest heart rate it sees while you're asleep. If not, then it will be the lowest one minute average it sees during the day. The value it records seems a little higher than I would expect, and I've seen some discrepancies when I'm wearing the [[Garmin 935]] and the Fenix 5X concurrently. I keep an eye on the reported resting heart rate, as this is a potential red flag for [[Overtraining]] or other health problems, but I'd only be concerned if I see a consistent rise over several days.* '''Move IQ'''. Garmin will estimate when you're performing an activity even if you've not explicitly recorded it. So, if I walk the dog, which I don't add to my training log, Garmin will automatically detect this as an activity.* '''Feedback'''. The area where Garmin really shines as an activity tracker is the feedback and inspiration that they provide. The Connect IQ watch faces can provide an overview of your weekly activity and how today is comparing with other days, which I find is a good way of motivating myself to get moving. Watch faces also provide a progress bar for how close you are to your daily step goal, though I wish that they'd implement some way of seeing your continued progress after you've hit the goal. Some days I can reach several times in my minimum goal, and it would be nice to see this visually. There are also a number of firework displays the watch gives when you hit your goal. These little firework displays could be considered cheesy or annoying, but I found over time that I really appreciate the little bit of positive feedback. You can also get more information on your activity by scrolling through the widgets on the watch, as well as a vast array of information and visualization on both the Garmin Connect smart phone app and their website.<gallery widths=200px heights=200px>File:Fenix 5X Activity12.png|The firework display when you hit your goal might seem a little cheesy, but I've come to rather like it.File:Fenix 5X Activity11.png|This is the display of [[Resting Heart Rate over the last week. This version is from the Fenix 5X, and compare with the next image from the Garmin 935.File:Fenix 5X Activity10.png|The Garmin 935 has a similar, but subtly different version of my resting heart rate.File:Fenix 5X Activity09.png|The step counting which it is a little uninspiring, but it does the job showing the number of steps and the daily goal.File:Fenix 5X Activity08.png|This display of the daily steps is nice, and the purple bar for Tuesday is showing that I didn't hit my goal that day (I was on airplanes most of the day.) I like this display, but the Connect IQ watch faces do it a little better.File:Fenix 5X Activity07.png|There is a similar display for the distance traveled, which is very accurate for the distance covered with activities that use [[Stryd, moderately accurate for those activities with GPS, and pretty vague if you just using the step counter.File:Fenix 5X Activity06.png|It's a little strange that this only shows the number of floors climbed, not those descended as well.File:Fenix 5X Activity05.png|This chart is one of the few places that show both floors ascended and floors descended. In my case, any mismatch is indicative of an error, as I don't use an escalator.File:Fenix 5X Activity04.png|The number of calories that the Fenix 5X thinks I've burned, both through activity and as basal metabolic rate (resting calories).File:Fenix 5X Activity03.png|This graph of active calories per day is rather nice, clearly showing the active and resting days.File:Fenix 5X Activity02.png|The number of activity minutes is something I find a little useless.File:Fenix 5X Activity01.png|You get a graph of activity minutes, but you can see on my resting days that hiking with a pack isn't enough to count.</gallery>=Training Advice (Firstbeat)=The Fenix 5X gives several types of training advice, and I'm rather skeptical as to their value. As George Box once said "[[All models are wrong| all models are wrong, but some are useful]], and for the Fenix 5X, and I'm not convinced the underlying models are good enough to be of practical benefit. Most of the training advice comes from software produced by [[Firstbeat]], and it relies heavily on accurate heart rate information. The optical heart rate monitor built into the Fenix 5X will degrade any of this training advice, so if you're interested in using this information, I'd recommend doing all of your training with an external, chest based heart rate monitor. In some cases, you also need to have your [[Maximum Heart Rate]] set correctly, which requires you to have it tested not estimated.<gallery widths=200px heights=200px>File:Fenix 5X 06.png|I've found the Firstbeat estimate of VO2max is generally pretty good for me, though it's no substitute for a true test. Changes in this VO2max estimate are used by other Firstbeat training metrics.File:Fenix 5X Training Effect.png|After each workout you'll see a display showing the training effect. This training effect is highly biased towards intensity rather than duration, as the quote from the Firstbeat paper indicates: "TE assessment considers continuous high intensity exercises with long duration to be the most effective".File:Fenix 5X Race Predictor.png|For me, the race predictor is a little optimistic, and you're far better off using a race result to predict performances at other distances.File:Fenix 5X Training benefits.png| The training benefit is hidden away in the menus, but gives another estimate of how your training session is affecting your fitness.File:Fenix 5X 03.png|I've found the training status information to be singularly unhelpful. It tells you whether your fitness at the load are going up, down, or staying the same, but gives you no indication as to what you should do about it. The help pages on the Garmin website gives some indications, such as "You can try increasing your training load to see improvement" for "detraining", but this should really be included with the watch itself. This Firstbeat training status uses both your predicted VO2max, and your training load changes as inputs to their calculations.File:Fenix 5X 08.png|The recovery time estimate is one of the more actionable bits of information, giving you an explicit instruction as to how you should train the next day. Sometimes this is useful, but all too often it gives me poor advice, including "train normally" after a brutally hard workout. The recovery time takes into account previous recovery time from prior workouts, so it's not looking at a workout in isolation.File:Fenix 5X 05.png|The training load is the weekly total of Firstbeat's EPOC values for all activities. EPOC is more of a measure of intensity, so this value is biased towards higher intensity workouts. It's unclear how the zones are calculated, but I'm assuming it's comparing the current value to historical norms. (EPOC is Excessive Post-exercise Oxygen Consumption, a measure of how much your metabolism is raised by a workout.)File:Fenix 5X 07.png|After the first 5-20 minutes of a workout you'll get an estimate of how recovered you are. The number reflects the change in the current estimate of VO2max from your baseline, so in this case it thinks my VO2max has dropped to 50. I've rarely seen any correlation between this value and how well I've recovered.File:Fenix 5X 01.png|Two minutes after you pause an activity, you'll get a report on how your heart rate has dropped. This can be a useful measure of how hard a workout has been, as a smaller drop suggests greater fatigue, though it's also influenced by fueling and heat.</gallery>=Navigation=The Fenix 5X has the best navigation features of any watch I've tested. Not only does it include full color maps, just like the [[Garmin Epix]], but it can even function like a typical satellite navigation system found in a car. He is a quick rundown of the features:* '''Full Color Maps'''. The Fenix 5X has preloaded maps of the US, and it's possible to download other maps (see details on the [[Garmin Epix| Epix review]]). * '''Breadcrumbs'''. During an activity, you will see where you've run as a breadcrumb line on the map. This allows you to backtrack or navigate a circular route that joins up with your earlier route.* '''Point of Interest'''. There preloaded lists of points of interest, allowing you to navigate to the nearest coffee shop, grocery store, restaurant, hospital, or whatever else you might need. You get turn by turn instructions, and you don't need any type of smart phone or network connectivity for this to work. This functionality is not available during a run.* '''Back to start'''. During go run, you can ask the Fenix 5X to navigate you back to your starting point, something Garmin calls "TracBack". * '''Courses'''. You can set up a course you like to follow and downloaded to the Fenix 5X and then follow that course during your run. I've found that incredibly useful when running ultras in situations where navigation is tricky. For instance, running along the trail that enters a campsite is a situation where it hard to know which trail to follow, or if you're on the right path as you leave the area. Another situation is where you are on a trail that has no turnoffs, so the organizers don't bother putting course markers out. This can be really unnerving, as you can't be sure there wasn't a turnoff that you missed, and having preloaded course brings a lot of peace of mind.* '''Compass'''. The compass provides useful navigation advice in some situations. With the GPS alone, you sometimes have to move a distance to be able to know the orientation of the map and reality, so a compass and give you your initial starting direction. I've had a number of runs in unfamiliar places where this is proved quite valuable.* '''Altimeter'''. Occasionally, an altimeter can provide valuable navigational insight, though typically you need a good topographical map to get much value from it. Knowing your current altitude can tell you if should you should be going up or down in order to reach a specific location.

The supports Fenix 5X/935 support a vast array of different sensors and accessories. It's the first Garmin watch range to support Bluetooth sensors in addition to Ant+ sensors, which opens up some new devices. The [[Connect IQ]] also makes the Fenix 5X extensible, allowing companies to add support for their devices themselves, rather than having to negotiate with the Garmin. We've seen this with both [[Moxy]] and [[Stryd]], proving the real-world value of this approach. Below are the various supported sensors and accessories, along with the results of my testing.

{| class<gallery widths="wikitable" style200px heights="margin-left: auto; margin-right: auto; border: none;"|- valign="top"200px>|[[File:Fenix 5X HRM Gauge.png|none|thumb|200px|A simple heart rate Gauge; it's pretty but not much more use than a simple data field.]]|[[File:Fenix 5X HRM Graph1.png|none|thumb|200px|Garmin's Heart Rate Graph is a [[Connect IQ]] data field and rather crude.]]|[[File:Fenix 5X HRM Graph2.png|none|thumb|200px|Here's the Heart Rate Graph in a smaller field. ]]|[[File:Fenix 5X HRM Altimeter.png|none|thumb|200px|This is the build in altitude graph, showing that Garmin can do better. ]]|}</gallery>

{| class<gallery widths="wikitable" style200px heights="margin-left: auto; margin-right: auto; border: none;"200px>|- valign="top"|[[File:Fenix 5X HRM GCT even.png|none|thumb|200px|One of the more useful Running Dynamics displays is the Ground Contact Time balance; imbalances are never a good thing. ]]|[[File:Fenix 5X HRM GCT off.png|none|thumb|200px|I find this display a little unintuitive as the arrow pointing to the right always makes me think my balance is in the red zone.]]|[[File:Fenix 5X HRM VR.png|none|thumb|200px|The display of Vertical Oscillation, Vertical Ratio, and Stride Length. ]]|}</gallery>

{| class="wikitable" style<gallery widths="margin-left: auto; margin-right: auto; border: none;"|- valign200px heights="top"200px>|[[File:Fenix 5X HRV (1).png|none|thumb|300px|Under the physiological menu…]]|[[File:Fenix 5X HRV (2).png|none|thumb|300px|… Is the option to turn on HRV logging.]]|}</gallery>

The Fenix 5X has first-rate support for the [[Stryd]] Footpod (see above), and also supports the standard [[Footpod]]'s. A standard Footpod will give better Cadence accuracy than the built-in accelerometer but to the Fenix 5X does a remarkably good job, and easy it's generally within a few steps per minute. The Fenix 5X also features a metronome to help improve your cadence, another really nice feature.

I've tested the [[GPS Accuracy]] of the Fenix 5X with its initial release the latest GPS firmware, and it's possible that its accuracy will improve as the firmware matures. Based on my testing, the Fenix 5X certainly has plenty of room for improvement. At best, the GPS accuracy could be described as mediocre, and I think it's bad enough that it could significantly mess up your training. If you look at the middle, curved section, you can see that the Fenix 5X is doing particularly badly here. This is a challenging section, and reveals any weakness in a GPS watch. The right most segment with the right-angle turn is a section of the most watches do reasonably well on, but the Fenix 5X is struggling here as well. The tracks don't look too bad, you can see that the Fenix 5X is not able to calculate the distance correctly. The Fenix 5X doesn't get too badly confused going under the bridge, actually looks a little better in that area than the two Suunto watches shown for comparison. The blue lap markers are rather widely spread, again giving more evidence of poor GPS accuracy. It's possible that other versions of the Fenix 5 might have different GPS accuracy. It's possible that the plastic 935 might do a little better, but without testing it's impossible to know. (I buy all my test gear through retail channels. This allows me to be brutally honest in my reviews, as I don't need to keep the manufacturer happy in order to continue getting free samples or early access. The downside is that I'm more limited in the array of watches I can test. Therefore, it's unlikely that I will test other versions of the Fenix 5 at this point.) I've tested both the 4.20 and the 4.30 version of the GPS firmware (see below for details.)

Remember ==UltraTrac Recording Accuracy==Like a number of other Garmin watches, the Fenix 5X supports Garmin's UltraTrac mode. This mode turns the GPS off periodically, and in theory it uses the internal accelerometer to estimate the distance. Garmin indicates that the accuracy should improve with use, but I've covered hundreds of miles since the last factory reset, so I think it's as good as it's likely to get. Unlike other watches that specify a regular polling interval, such as every 15 seconds, UltraTrac does not specify the interval. I have recording set to every second, and the Fenix 5X records location information that's updated each second, though it's obvious from the track shape that it's interpolating from periodic polling. I think that the overall firmware version number doesnaccuracy seems to drop after a few hours, but I can't be sure as I don't influence have enough data to do a statistical analysis. As you can see from the table below, the GPS Accuracy with UltraTrac is predictably grim. This is not unreasonable, given this is clearly trading off accuracyfor battery life. (I've used percentage errors rather than the scores I've used above as the level of error in UltraTrac messes up my score calculations.) {| class="wikitable sortable"!Device!Accuracy<br/>(Combined)!Trueness<br/>(Average Distance Error)!Standard Deviation<br/>(From mean)!Standard Deviation<br/>(From true)!Repeatability|-|Fenix 5X 4.30 Normal GPS|style="background-color: #B1D47F;"|4.44% (234.5 Ft/Mile, 44.4 m/Km)|style="background-color: #A4D07E;"|3.12% (164.6 Ft/Mile, 31.2 m/Km)|style="background-color: #EBE582;"|4.33% (228.7 Ft/Mile, 43.3 m/Km)|style="background-color: #BCD780;"|5.45% (287.9 Ft/Mile, 54.5 m/Km)|style="background-color: #DAE081;"|3.24% (171.1 Ft/Mile, 32.4 m/Km)|-|Fenix 5X 4.30 UltraTrac|style="background-color: #F8696B;"|15.92% (840.7 Ft/Mile, 159.2 m/Km)|style="background-color: #F8696B;"|14.62% (772.1 Ft/Mile, 146.2 m/Km)|style="background-color: #FDBA7B;"|6.40% (337.8 Ft/Mile, 64.0 m/Km)|style="background-color: #F8696B;"|17.12% (904.2 Ft/Mile, 171.2 m/Km)|style="background-color: #FB9F76;"|5.93% (313.0 Ft/Mile, 59.3 m/Km)|}As you'd expect, the GPS tracks show the typical straight lines you get from periodic GPS polling. You have 'll notice however that the GPS is turned on long enough to look get several readings as there are various wiggles and loops at the corners of the track lines. {| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"|- valign="top"[[File:BridgeFenix 5X 4.30 UltraTrac.jpg|center|thumb|x300px|The shape of the GPS firmware numbertracks under UltraTrac.]]|- valign="top"|[[File:BridgeFenix 5X 4.30.jpg|none|thumb|x300px| For comparison, here's the tracks from the normal GPS mode.]]|}==GLONASS Accuracy==With GLONASS enabled, the Fenix 5X demonstrates even worse performance than its peers. The values shown below are rather dramatically worse with GLONASS enabled than without. My anecdotal observation is that sometimes the Fenix 5X does a little worse with GLONASS than normal, possibly in line with other Garmin devices, and sometimes it seems to just get lost and produce dramatically worse results. {| class="wikitable sortable"!Device!Accuracy!Trueness!Precision!Repeatability|-|Fenix 5X 4.30|style="background-color: #FEC97E;"|5.6|style="background-color: #EDE683;"|6.9|style="background-color: #FCA377;"|4.5|style="background-color: #F3E783;"|6.8|-|Fenix 5X 4.30 GLONASS|style="background-color: #F97B6F;"|3.5|style="background-color: #FFE082;"|6.2|style="background-color: #F8696B;"|1.6|style="background-color: #F97B6F;"|3.5|}Below you can see a visual representation of the problems. Many of the tracks are a little worse than normal, but you generally follow the path. A small subset of the tracks are dramatically worse, either showing and offset from the actual path, or sometimes it looks like the sampling frequency has dropped, suggesting that the watch is only periodically able to get a location fix. This latter phenomenon is rather surprising to me and goes against my hypothesis of why GLONASS has worse accuracy. I would expect there would be more satellites available with GLONASS enabled, which would result in the watch selecting the subset with the strongest signal that are more likely to have a narrow angle of separation, which would result in increased Dilution of Precision (DoP). These tracks suggest that the Fenix 5X Firmwareis unable to get any location fix for brief periods. {| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"|- valign="top"|[[File:BridgeFenix 5X 4.30 GLONASS.jpg|center|thumb|300pxx300px| The GPS tracks from the Fenix 5X with GLONASS enabled. This diagram has tracks color coded with green indicating good accuracy through to red indicating poor accuracy, and the lap markers as blue dots.]]|- valign="top"|[[File:BridgeFenix 5X 4.30.jpg|none|thumb|x300px|Here's where the version tracks from testing with GLONASS disabled for comparison.]]|}==GPS Problems==As I note in my main article on [[GPS Accuracy]], most watches have "bad days" but I've found that both the F5X and the [[Garmin Fenix 5X Plus| F5X+]] have a disproportionate number of these problems. These "bad days" are not a general degradation of accuracy, but represent the watch either completely losing the GPS firmware signal and recording a straight line, or zigzagging wildly, resulting in a massive error. I exclude these "bad days" from my results to ensure they don't skew things. However, I had a disconcerting cluster of these "bad days" and I really thought I had a hardware issue with my F5X, something that's remarkably improbable. (Hardware issues don't typically result in degraded accuracy but complete failure to acquire a signal.) When I started testing the F5X+ alongside my original F5X and saw similar issues with both units (though not at the same time) that I realized this is locateda more systemic issue. To see if this is a general GPS issue, I verified the accuracy of the Fenix 3 and the 920XT alongside the F5X/F5X+ and both the F3 and 920XT were fine. Then for no reason I can ascertain, these "bad days" went away.]]

I've not found any [[Optical Heart Rate Monitoring ]] (OHRM) implementation that's good enough to be useful, and the Fenix 5X is no exception. I believe that you're better off having no heart rate data than bad heart rate data. While a chest strap based heart rate monitor can have accuracy issues, these are generally dramatic and obvious, whereas OHRM can be quite misleading. (The issues with a chest strap heart rate monitor are also usually fairly easy to remediate, either with some electrode gel or a new battery.) The accuracy of [[Optical Heart Rate Monitoring]] (OHRM) will depend on a number of factors:

{| class="wikitable" style<gallery widths="margin-left: auto; margin-right: auto; border: none; "|- valign150px heights="top"150px>|[[File:Fenix 5X Stryd Add (1).png|none|thumb|100px|From the watch face, long press on the up button and then scroll to the settings menu and enter.]]|[[File:Fenix 5X Stryd Add (2).png|none|thumb|100px|Scroll to sensors and enter.]]|[[File:Fenix 5X Stryd Add (3).png|none|thumb|100px|Enter on add new]]|[[File:Fenix 5X Stryd Add (4).png|none|thumb|100px|Scroll to footpod and enter (don't search for all as you don't want to add as a power pod.)]]|[[File:Fenix 5X Stryd Add (5).png|none|thumb|100px|Hopefully Stryd is the only footpod in range, so hit enter to add.]]|[[File:Fenix 5X Stryd Add (6).png|none|thumb|100px|Once added you'll bounce back to the list of sensors. Hit enter to configure.]]|[[File:Fenix 5X Stryd Add (7).png|none|thumb|100px|Scroll to Speed which will be set to indoor, hit enter to change.]]|[[File:Fenix 5X Stryd Add (8).png|none|thumb|100px|Scroll to always and hit enter.]]|- valign="top"|[[File:Fenix 5X Stryd Add (11).png|none|thumb|100px|Confirm speed is now always.]]|[[File:Fenix 5X Stryd Add (9).png|none|thumb|100px| Scroll to Distance which will be set to indoor, hit enter to change.]]|[[File:Fenix 5X Stryd Add (10).png|none|thumb|100px| Scroll to always and hit enter.]]|[[File:Fenix 5X Stryd Add (12).png|none|thumb|100px| Confirm distance is now always.]]|[[File:Fenix 5X Stryd Add (13).png|none|thumb|100px|Scroll to calibration factor and hit enter.]]|[[File:Fenix 5X Stryd Add (14).png|none|thumb|100px|Scroll to "auto calibrate" and hit enter]]|[[File:Fenix 5X Stryd Add (15).png|none|thumb|100px|Scroll to disable and hit enter.]]|[[File:Fenix 5X Stryd Add (16).png|none|thumb|100px|Confirm calibration is 100.0]]|}</gallery>