myBPM is a tool for getting the Beats Per Minute of Music, your heartbeat or whatever there is with a regular sound. It will show you the average BPM of up to 100 taps, which results in an high accuracy.
The offset shows you the milliseconds your last tap was off compared to the average BPM. The offset Δ shows you the average offset of your taps.
The values are stored until you hit the „Reset“ button to start over. There is no automated reset and that is on purpose.