My Garmin 645 Watch Is A Lying Liar Who Lies

June 16, 2021 10:44 AM

I’ve been tracking my running with a Garmin watch for the last year or so, and have found it very useful. This week, though, I’ve been staying with a friend who tracks his with an Apple Watch, and on two runs together, we have significant differences in elapsed time, distance, and speed when we were running right next to each other for exactly the same time and route.

On one approximately four mile run (4.0 by my watch, 4.15 by his) his watch showed a pace almost a full minute per mile faster than mine. A later run was less extreme, but still showed a 20s per mile difference in pace.

Anyone know what gives? Is this idiosyncratic, or is there a known discrepancy between paces measured by Garmin and by Apple? Anyone know which is likely to be accurate? (I would love for the Apple Watch to be the accurate one, because I will then have suddenly become much faster than I thought I was.)

posted by LizardBreath to Health & Fitness (12 answers total)

Some things to check:

Are you waiting at the start of the run to ensure the watch is connected to satellites?

Is there an autopause set? If you are starting and ending the watches at the exact same time and the elapsed time is different, this can be because one person's watch is set to pause the time when the user is stopped at corners, traffic lights, etc.

What happens when you upload the data to something like Garmin Connect or Strava? Is there a blip on the line? GPS watches aren't infallible. Sometimes a rogue reading gets in and when I look at the actual route run, there is a blip off on another block. This happens less now than fifteen years ago.

Have you looked at the uploaded route paths side-by-side?

Have you mapped the uploaded route path on Google Maps and compared that?
posted by TORunner at 10:57 AM on June 16, 2021 [2 favorites]

This data is a little old but shows how pace can vary pretty dramatically on different devices: https://fellrnr.com/wiki/GPS_Accuracy. Interestingly, the Apple Watch that he measures is in the middle, measuring more accurately than some Garmins but less accurately than others. The biggest factor affecting accuracy will be how often the watch registers your position -- Some watches will have a power saving setting which will make them less accurate (by taking your position less frequently), so it's worthwhile to check if you have that turned on - or your friend may have something similar turned on on their Apple Watch. This can especially affect how accurate the data is if your course has a lot of turns - if your position is being measured less frequently, it will show you being slower, since it will register you as cutting the corners of the turns.

FWIW after seeing this data I caved and bought a footpod - I love it but it's 100% a ridiculous gadget for me to have.
posted by matcha action at 11:00 AM on June 16, 2021 [1 favorite]

I am a Garmin runner; my wife uses an Apple Watch. We run at different paces but our splits seem reasonable (and consistent) from run to run. I'd be inclined to give Garmin the edge for accuracy in measurement because....well no good reason except that they're Garmin and GPS has sort of been their thing forever.

That seems like a big difference though, so on preview, check TORunner's bits for some sort of wierdo thing with the data.
posted by jquinby at 11:01 AM on June 16, 2021 [2 favorites]

If the elapsed time is different it almost has to be auto-pause on one and not the other.
posted by ftm at 11:05 AM on June 16, 2021

Response by poster: Not to threadsit, but both times we had indistinguishable maps on Strava — the lines on the map looked the same, but the Apple Watch measured it as a longer distance and also believed less time had elapsed. No more than a few seconds pausing at crosswalks either time.
posted by LizardBreath at 11:05 AM on June 16, 2021

DC Rainmaker does some extensive testing around the GPS accuracy of the various units, including testing multiple watches and headunits on the same run to see comparison.

The Garmin 645 review is here and a look at the Apple Watch Series 6 is here .
The Garmin 645 essentially is accurate, as is the Apple Watch series 6. If your friend doesn't have a series 6 but one of the earlier model then they tend to do a lot of "smoothing" of the routes which results in the track cutting or overshooting corners. Still probably not enough to make the differences you noticed unless you are really doing lots of corners.
posted by Mattat at 11:33 AM on June 16, 2021 [2 favorites]

Sorry - botched the link. Apple Watch Series 6 look at accuracy is here
posted by Mattat at 11:46 AM on June 16, 2021

Garmin has an auto pause feature that can stop your watch from timing if you stop or go below a certain pace.

Garmin also has as smart recording feature that takes fewer measurements to make the battery last longer.

Apple watches might have similar features.

Also, this doesn't explain the total time elapsed difference but you'd expect your pace to be different if the total distance measured is different. Say you ran for 40 minutes and your watches measured 4.0 and 4.15 respectively. Then the longer distance had a 9:38 pace and the shorter one had a 10:00 pace.
posted by carolr at 11:59 AM on June 16, 2021

A run's pace is just time divided by distance so it should be clear where the differences lie. If you are starting and stopping at the same points and times then the paces should be the same. If they are not then somebody's GPS should be off and showing more or less distance on the respective app maps. The other possibility is that your friend has a pause autodetect. My garmin has this - it vibrates and shows a pause on the watch face over the display until I return to a running pace.

If you run with your phone you can compare route maps between your phone app, your gamin and Google Maps' Timeline feature. They are almost always slightly different! I run on the Chicago lakefront but I start near a bunch of towers. The weird part is that both my phone using runkeeper and my Garmin watch handle the start fine about 95% of the time if I give them time to locate the satellites (I use an app called GPS Status that lets me see what is going on GPS-wise on my phone because it used to have trouble getting a GPS signal). But when I run out on the lakefront trail away from the towers I get crazy ass half-mile GPS jumps across harbors and such that show up on my phone and whatever tracking app (Endomondo and Runkeeper) I use. The Garmin however is rock solid for me even just the watch without any post-hoc phone or backend smoothing.

If you zoom in on any run tracker app's map you can usually see some GPS wobble where it will have you running zig-zags like Rickon Stark should have but absolutely no sober runner ever does.
posted by srboisvert at 12:13 PM on June 16, 2021

Best answer: If you can get a list of the time-stamped GPS coordinates being recorded by the devices, I bet you'll see that yours is recording with lower frequency than his. E.g., his has a datum every 1 second, and yours is every 10 seconds. When the devices try to estimate distance, they have to fill in the gaps between those, and the easiest way to do that is with a straight line. Which means that yours is literally cutting corners --- smoothing your route a little bit in a way that reduces its length. That also explains the pace difference, since your device thinks you're covering less distance in the same amount of time.

You can test this theory by running one route that's as straight as possible (which should decrease this error), and then running one route that has a lot of sharp corners (which increases it).
posted by qxntpqbbbqxl at 1:41 PM on June 16, 2021 [9 favorites]

Ah, interesting - the 645 (and others) have this as a configurable option:

Data Recording

Sets how the device records activity data. The Smart recording option (default) allows for longer activity recordings. The Every Second recording option provides more detailed activity recordings, but may not record entire activities that last for longer periods of time.
posted by jquinby at 1:52 PM on June 16, 2021 [2 favorites]

I find it really strange that your maps on Strava were identical, because it's horribly zig-zaggy where I live. My daughter and I often are quite amused at how different our two (exactly the same) phones (with same service) map out on Strava, and then both of our Fitbit paths are different than those. A couple more trackers I've tried give yet more variations. It's ridiculous, honestly.

And these are on relatively straight-lines paths, long sides of a rectangle or square. Using a 1/4 mile-ish track REALLY makes a mess of things, and an exact one-mile walk shows as about 1.12-1.25.
posted by stormyteal at 2:01 PM on June 16, 2021