We measure the amount of time (gap) between the start of the drive in stroke 1 and the start of the drive in stroke 2. We then take a rolling average of those gaps and extrapolate that over 60 seconds to calculate the SPM.
- Gap between stroke 1 and stroke 2 = 2.5 seconds
- Gap between stroke 2 and stroke 3 = 3.5 seconds
- Average gap = 3 seconds
- Extrapolated SPM = 20 (60 divided by average gap in seconds)
