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{{DISPLAYTITLE:Polar M400 Review}}
[[File:Polar M400.jpg|right|thumb|200px|The {{Polar M400}}.]]
The {{Polar M400}} is a disappointing watch, with poor GPS accuracy and limited support for [[Cadence]]. Even at its low price point it I don't think it offers good value for money. If you're after a midrange GPS watch, I'd suggest looking at the [[Garmin 610]]. While it's an older watch, it offers far more features than the M400. The Garmin 220 is more expensive, but offers better functionality.
=Polar M400 Pros=
* The user interface is nicely designed and intuitive; the buttons, display, and the menu system combine aesthetics with usability. The M400 has five hard buttons, which I much prefer over a touchscreen interface, especially when wearing gloves or in the rain.
* The cable to charge and sync the M400 is a standard micro-USB that's waterproof. Most watches use a specialist cable that's expensive to replace if lost.
=Polar M400 Cons=
* Polar has added support for a [[Footpod]] with version 1.4 of firmware, but this is problematic.
** The Polar Stride Sensor is fully supported by the M400, with automatic calibration and it will display stride length as well as cadence. However, the Stride Sensor is huge and heavy when compared with modern Footpods, weighing over three times as much as a Garmin Footpod. Because of its size and weight, it requires lacing into the shoelaces, making it a real pain to move between shoes. <jfs id="B00CCASIMS" noreferb="true" n="Polar Stride Sensor"/>
* '''WiFi/Bluetooth Uploads'''. While the automatic upload of workouts via WiFi or Bluetooth to a Smartphone is nice, the upload will typically only go to the manufacturer's web site.
{{BuyAmazon|AZID=B00NPZ7WNU|AZN=Polar M400}}
=GPS Accuracy=
The M400 has the worst GPS accuracy of any device I've testing.
* Both Trueness and Precision are remarkably poor. The M400 is nearly always giving a shorter distance than I actually ran, over 250 feet/mile on average.
* The M400 does a better on repeatability, which is a measure of how likely it is to give the same indicated distance on a particular part of the course. This tends to give an illusion of being correct, as it is easy to mistake consistency for accuracy.
* An out-and-back turnaround is challenging for any GPS watch, and this often shows up the difference between a good and bad a device. A really good GPS watch will typically be out by 2 to 3%, but the M400 does particularly badly with an error of over 13%.
* Running in a straight line on the other hand, is a fairly easy task for most GPS watches, and hear the M400 does vastly better than in other conditions. However, when it's compared to other devices, it's still one of the worst.
* Rather strangely, the M400 does remarkably well going under the bridge. It's almost like it does better without the GPS signal than with it. If you look at the image below and compare it with the V800, you can see the M400 does much better when emerging from under the bridge.
* While I rely on detailed measurements and statistical analysis to evaluate GPS accuracy, it's worth mentioning that on one 18 mile run the M400 has lost over a mile. This is the worst a level of error I've seen, even worse than the [[Garmin 620]] before Garmin fixed their problems with a Firmware upgrade. (I tested the M400 with version 1.4 of the firmware and the GPS accuracy is unchanged.)
* It looks like Polar are using a different GPS chipset in the M400. The V800 uses the SiRF chipset, where the M400 uses [http://www.u-blox.com/en u-blox].
* I have seen the Polar M400 losing satellite signal with the message "There's no GPS signal". This occurred under conditions where another device is doing fine and there are not circumstances that would cause a problem.
{| class="wikitable"
|- valign="top"
|[[File:BridgePolar M400.jpg|none|thumb|x300px|This image shows the tracks from the M400 color coded for accuracy. You can see a few tracks where the M400 has shifted out of position even though the shape of the course is maintained. The blue lap markers are quite spread out, suggesting some positional accuracy problems. You can see from the green lines going under the bridge that the M400 does quite well in that situation, and there are no sudden changes in position on emerging. I suspect this is because the M400 is doing a lot of smoothing, which works well in that situation. The middle segment that is quite curved is nearly all red, and this is one of the areas where the M400 is a smoothing too much and cutting the corners. You can see the M400 does worse here than in the sharp turn to the right of the image. ]]
|[[File:BridgePolar V800.jpg|none|thumb|x300px|The Polar V800 is one of the most accurate devices I've tested, and you can see that the majority of the tracks are green indicating good accuracy. Notice the problems the V800 is having at the bridge. Rather strangely the lap markers are far more spread out than I would have expected on a device this accurate. ]]
|- valign="top"
|[[File:AccuracyPolar M400.jpg|none|thumb|x300px|This is a detailed image of a small zigzag in my course, that shows up how well a device is tracking. You can see a mixture of colors from green indicating good accuracy through to read indicating poor accuracy. Notice that the M400 is typically tracking the shape of the six ag but is often out by a fair distance. If you were to shift the tracks so the blue lap marker was positioned over the red spot that indicates the true map position you'd probably find things lined up much better.]]
|[[File:AccuracyPolar V800.jpg|none|thumb|x300px|The Polar V800 follows this small zigzag quite well. The overwhelming majority of the lines are green indicating a good accuracy, even though the lap markers are quite spread out. ]]
|- valign="top"
|[[File:ZigZagPolar M400.jpg|none|thumb|x300px|Here is the zigzag with the M400 tracks color-coded for direction, with green coming from the right, blue from the left. Typically GPS watches record tracks that have the green lines shifted slightly down and to the left, blue up and to the right. However the M400 appears to be a little more random than that.]]
|[[File:ZigZagPolar V800.jpg|none|thumb|x300px|As you would expect from a device as accurate as the V 800, the tracks are close together and follow the line of the zigzag nicely.]]
|}
=Comparison Table=
{{:Best Running Watch-table}}