Watch and Fitness App: Pool Swim Inaccuracies with lap counts and distance calculation
I recently got an Apple watch (series 6, O/S v7 ), and started using it to track my pool swimming workouts. While it's amazing how much engineering has gone into this device, I'm having accuracy issues with its lap counting.
I researched how the watch counts laps, which I now believe it does strictly by marking your turns at each end of the pool. Lap counts have nothing to do with the "pool length parameter" you provide as input to the "pool swim" workout in the fitness app, at least according to Apple's director of engineering for motion services (Ron Huang), quoted in this article. That's not necessarily intuitive, and even Apple's support article, contains contradicting information indicating that the pool length parameter does affect lap counting. However, I'm fairly certain Huang is correct and the support article is just poorly worded: "...be sure to accurately set the pool length to help your Apple Watch measure laps and distance".
But what is the definition of a lap? Is it the same as one length of the pool, or to the far end and back again? To my surprise, this is a question of some debate. Shockingly, this isn't even mentioned in the support article or any of the articles on the watch I've read!! However, I think this settles that, and a lap is one length of the pool, not two lengths.
Interestingly, my freestyle strokes are counted by the fitness app as just below 50% of the actual laps I count, where 1 length=1 lap. Perhaps Apple was using the "other" (as in wrong) definition of a lap? But then I learned laps were counted by marking turns based on the watch's motion data, therefore each turn, i.e. each length of the pool, marks a lap. On my second swim day, I paid more attention to the counter at the start of my swim, and noticed after about 8 laps, it was still at 0, that's problematic! I think it started counting around the 10th length/lap, huh? Ok, maybe it needs to tune its algorithm, but you would think it would estimate lost laps, not just leave them as uncounted!
I was impressed by the fact the watch also knew my stroke type, which had only been freestyle on my day 1 swim. So I added 20 laps of breast stroke to the end of my swim on day 2. With breaststroke it was easier to monitor my watch, and to my utter confusion, it was counting every single length as a lap, with perfect accuracy.
Explanation? If marked turns are how laps are counted, and turns are marked by analyzing the motion data generated from the arm wearing the watch, and arm motions vary by stroke type, then how one "turns" will affect lap accuracy. I'm not doing flip turns with my freestyle, and my freestyle turns are definitely less consistent than my breast stroke. I just wish I knew how to modify my freestyle turns to get better lap count accuracy. Right now it's a mess, with freestyle at just under 50% of actual, and breast stroke being accurate.
Now, as if all of this wasn't confusing enough, there appears to be a bug in how the Fitness app reports on the total distance traveled. Granted, if the laps count is wrong, the distance calculation can't ever be right. But simply multiplying the app's own reported laps (99) by its known pool length (7m), does not even match its reported distance (724m)! See inserted screen shot. Madness!!!
Two last points about distance. If pool length is a key parameter for calculating total distance, then why is the smallest unit of measurement a yard, as opposed to a foot? Private pools are not created in even numbers of yards. A 25 foot, 8.3 yard pool would have to be rounded to 8 yards. I am swimming about 200 actual laps leading to a distance inaccuracy of 200 x 0.3 yards, or 60 yards, or 180 feet, not insignificant and unnecessary. Unless we are being dissuaded from assuming accuracy by preventing a smaller unit of measure?
Lastly, there are 3 pool swim goals (calories, distance and time). Most swimmers measure progress using either distance or laps. Distance is clearly flawed, and there is no "laps" goal. Mentally counting laps (for either a lap count or distance goal) is actually rather difficult without losing one's place, especially when swimming a couple hundred laps. I really hoped the watch would be able to count for me, so I can focus on swimming (or day dreaming)!
The watch is absolutely amazing, counting swim laps is insanely difficult, and Apple engineers have certainly spoiled us with toys, raising our expectations ever higher each year. I'm hoping those brilliant engineers might eventually teach us how to help the watch do better, if we possibly can. And we need the Fitness app report developers to fix their reporting: let us input more accurate lengths, and report total distance to agree with laps x length.
Apple Watch
