Tempo 

When the Tempo button is turned on, a digital readout will appear in the upper-right corner of the video. 

The number displayed here represents the time (in minutes, seconds, and thousandths of a second) elapsed since the first key position (“address” in golf). Therefore, in order for the tempo feature to operate effectively, you should accurately set the first key position for your video. 

You will see negative numbers here if your video includes motion before the first key position.