Have you timed your 100m dash ? What is the best way to do it since the granularity is very important?
Stopwatch in your hand. If you really care about the milliseconds here’s a handheld one SC SPORTCOUNT Compact Stopwatch Swim Timer - Waterproof Handheld Swimming Stopwatch for Timing Competitive and Recreational Swimmers in the Pool https://a.co/d/dzziV0e
Or have someone clock you with a stopwatch. Ask a gym employee, I’m sure they’d step outside and stand on a finish line for you
Now or peak
10.88. Go online (usatf) and find an all comers meet.