GPS Accuracy-Apple Watch vs. Garmin

GPS Accuracy-Apple Watch vs. Garmin: a reader asks…

I’m using a Garmin watch to measure distance on a golf course. A buddy of mine is doing the same but with his Apple watch (using The Grint app). While our two devices are reasonably close, they’re sometimes a good 10 yards off of each other. Using one measurement might make me change clubs versus the other. Should I trust either watch?

GPS accuracy can be hit or miss with small devices, depending on a lot of variable factors. For one, it may take several seconds to a minute or more before either device processes enough satellite signals to get a reasonably accurate result. For another, trees, your body, and even thick clouds can affect reception of the satellite signals by your watch. The more satellites your watch can see (line of sight with no obstructions), the more accurate it will pinpoint your location. All things being the same, the two devices should be within 10% of each other.

Sometimes moving just a few feet one direction or another can make a big difference in the reading. While it only takes three visible satellites to triangulate a fix on your position, your device can use as many as eight satellites to get a really accurate reading. The more satellites your device can see, the more accurate your fix. If your Garmin and your buddy’s Apple Watch are more than 10% different, try moving around a little, and then give it a good minute in each position to compare – it can take that long for your watch to acquire and calculate your position with new satellites it couldn’t see before.

Your golf course will have markers usually set in the ground near a tee box, and if you stand on one while reading your position, you can gauge the accuracy of your position fix. Rotate around slowly holding your watch away from your body and see if/how the distance to hole changes. Both the Garmin and the Apple Watch (using various golf apps) will give you a range and the marker you’re standing on should be in that range. If you see the numbers change by more than 5-10 yards as you rotate, then you know there’s some interference with one or more satellites. That could be due to your body being in the way, or surrounding trees.

These GPS devices aren’t meant to be as accurate as military applications, but either should give you a rough idea of the distance to the hole. Take their measurements with a grain of salt, and trust your instincts – if the hole looks a lot closer or further than the watch reads, choose your club based on your gut, not the watch.