I'm probably half a count off i'm guessing. Are you saying all your 10swing times are within .01 seconds of each other over the 100 swing period?
How are you hanging your racquet and what is the angle you are releasing at?
I have mine on 2 screwdriver cylinders, the types they use for glasses so they are pretty low on friction i think. I use about a 15 degree angle (The racquet will swing off-axis if the angle is too high depends on how coordinated and how good your setup is ). I wait for it to swing a few times before starting the count. The total error the app estimates is usually .002s sometimes it will give a .004s error which i don't use that result.
BTW since we have the same racquets I measured my hang distance at 64.3cm with 17 gut strings, curious if we have the same hang distance.
I always think my measurements are off.
@Aretium
Pretty much every method that gets swing measurements by hanging off the top mains uses the same parallel axis formula, the accuracy depends on how well your setup is, and measurements.