Health App Inaccurate Distance

Just thought you might be interested in knowing ...

The "Walking + Running Distance" measured by the Apple Health app is somewhat inaccurate. This has been the case for several iterations of the app, and on different iPhones, and continues in iOS 11.1. The error varies but is generally about 10% less than the actual distance walked/run. (Good news for folks who use the Health app for measuring your workout - you've gone farther than you think!)

How do I know the app is inaccurate? I've used the app on very accurately measured flat walking/running paths (including a 1/4 mile track, a bike path, roads, etc.), and the app is consistently about 10% short of the actual distance.

Perhaps more importantly, this doesn't appear to be a hardware issue. The MapMyWalk app is very accurate, to within a few yards of a mile, and the Apple Health App is always 5% to 10% short of the actual distance and the distance measured by MapMyWalk. Seems there's something odd about the way the Health app interprets/uses GPS readings.