My garmin forerunner is also very accurate. Just strava is inconsistent for me.My ”system“ is to set my Apple Watch (series 4) bicycle workout and compare its gps distance with my Allant’s Purion mileage or even what the trail map says. So far they are very close to one another. The watch/iPhone maps the route as close I’ll ever need, gives me splits, elevation gain, average mph, heart rate, time of ride, yada, yada. If I was like some and was just trekking out in the wild, I might consider a more accurate system.