Inconsistent Distance via Health App

There are lots of threads on this topic on the Apple forums and on forums across the Internet. But I've been encouraged by a high-level "expert" to start yet another one, so here it goes.

I've seen no official Apple feedback on this issue, but high-level forum posters often claim that the Health app uses GPS to calculate distance. I don't see how this can be true, since my wife and I often--daily--walk together side by side and get dramatically different results on our identical iPhone 6s's bought at the same time and running the same version of iOS. The Health apps are set up the same way, with the same input sources. Yet, for the same walk, her mileage total is usually 10-20% higher than mine. It's sometimes a little more, sometimes a little less, but it's never the same. The GPS on both phones appear to work just fine; for example, they indicate the same locations when using Google Maps.

It is feasible that the Health app uses GPS in combination with other things, like the accelerometer. In fact it seems likely: Otherwise, how could Health distinguish between walking and, say, riding a bike, or riding in a car? If it isn't bouncing, it doesn't count as walking. Could it be that I walk too smoothly? Don't bounce up and down enough?

This has been discussed on forums for years. I'd say it's time someone, maybe someone from Apple, provided a definitive, convincing answer, ideally with some references or technical information to back it up. Alternatively, maybe someone can help me find a fix for the obviously malfunctioning iPhone/app. Only problem is, I don't know which one is malfunctioning, hers or mine?

Thanks to all.

Jim

Message was edited by: James C Austin Fixed a typo.