Distance per Stroke

DPS is first calculated by lap, then averaged over the swim. So if you swim 200m in 98 strokes the DPS isn’t simply 200/98.  The reason for this is, on a lap by lap basis, you can have 1 arm do +1 extra stroke per lap, so by the end of the 4 laps your right arm could by at 98, but left at only 94.

So I first calculate the DPS for each lap.  If for example you do 28 right and 27 left in the first lap of a 50 m pool it will calculate the DPS as:  50m /28strokes = 1.79m/stroke

It will do the same for lap 2, 3 and 4, then find the average of the four and report the DPS of the swim as the average.

There are some known flaws in the DPS metric:

1. It doesn’t incorporate the distance the swimmer pushed off underwater.  So if you push off for 10m underwater and do 28 strokes then your DPS should really be 40m / 28 strokes = 1.05m/stroke. Unfortunately, our IMUs don’t have the ability to allow us to detect the distance travelled underwater.
2. In freestyle/backstroke, the number of strokes between left right isn’t always even, I’m taking the largest of the two for the lap.