How Accurate is Strava vs Apple Watch vs Laser Rangefinder???

 Educated as a Mechanical Engineer and trained as a Six Sigma Black Belt, I love data.  Data is neither good nor bad.  It is just data.  And as long as it's collected accurately and properly, it cannot be refuted.  You may like it or not, but that's a human emotion you attach to the data.  There is just no arguing with data.  It is what it is.  Based on that, I wanted to know why my Apple Watch Ultra II, Strava, and my Sig Sauer rangefinder do not agree on distances...

I have a thousand-yard range set up on my property.  I know exactly how far 880 yards (one-half mile) are from the target to direct line of sight of my marker.  Well, to within 1 yard (3 feet) as sighted by my Sig Sauer Kilo 2200 BDX rangefinder.  This Kilo model is accurate to within 1.5 feet out to 500 yards and to within 3 feet (1 yd) beyond 500 yards.  So when the rangefinder, using Lightwave DSP Technology, says my marker is at 880.1 yards, I believe that I am somewhere between 879.1 and 881.1 yards.  Again, direct line of sight to my target.  So, if I walk from my marker to the target and back, that should equate to 1 mile walked (plus or minus 2 yards).  However, this does not account for the variation in terrain.  So if I must go up and/or down (say thru a ditch) to get to my target, the actual walking yardage could be further, and in fact I will suggest that it is.  Also, there is a zero probability that I can walk in a straight line, like a laser, to and from the target.  A bullet, mind you, does not have to make such corrections as it is not walking up or down the same terrain amd will follow a straight path.

Thus, I conclude that if I start at 880.1yards (plus or minus 1 yard) walk to my target and back, I will have walked at least 1,760 yds (one mile) and probably more.  To test this hypothosis, I stood at 880.1 yards away from my target and started my Apple Watch Ultra II and Strava for an outdoor walk.  Then me, the wife, and the puppy started down range.

Strava and the Apple Watch kept to within 0.1 mile over the entire course, with the watch being consistently behind - showing a shorter distance walked.  However, this difference was insignificant being only 5 yards before both systems agreed to distance.  And as you can tell from the photo below - I most certainly did not walk a straight line and I also had to travel up and down.  So it should come as no surprise then when the One Mile mark came from Strava, I was not back at the starting point.  And then 5 yards later, my Apple Watch ticked One Mile.  When I finished, I was 10 yards from my 880.1 mark.



How does Strava calculate distance?  Strava uses GPS but only after uploading the signal.  This assumes a flat terrain, but makes up for it by eliminating stuck points.  There is a great Strava support article on this here:  How Distance is Calculated – Strava Support

The Apple Watch distance calculator?  It also uses GPS but calculates distance based on steps and an internal accelerometer.  This is highly dependent upon the user inputs of height & weight.  Get those wrong and your measurements are going to be suspect.  But the Apple Watch does make corrections over time - thus becoming more and more accurate the more you use it.  Again, assuming you have entered the proper personal data.  

And just for fun, I grabbed the data from my dog's Tractive GPS Smart Tracker - that uses cellular data.  Mind you, in power saving mode, this tracker only uploads ever 7 minutes.  Yes, you can force a live signal and get more accurate data, but you really don't need to.  On this same route, Tractive said we walked 0.65 miles.  This is entirely expected. 

Conclusion:  MY Apple Watch and Strava are within 5 yards (15 feet) or 0.28% of reading the exact same distance over a one mile course (your experience may be different).  My expectation was that they would be farther apart than that due to how each calculates distance.  I am confident that accurate personal data must be typed into the Apple Watch for you to receive the same results.  

And folks, at the end of the day does any of this really matter?  I suggest not.  It matters that you are out there getting after it regardless of the method you utilize to track the distances.  Apple Watch, Garmin, Strava, or any other method.  Just go and remember to have fun along the way.


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