When you need to sync the S2400 to a non MIDI instrument (like turntables), tap tempo is a good tool to find the BPM of a track, but you may need to push forward or backward the tempo to perfect match, like with a turntable.
It could be done with keeping tempo pressed, then >>> or <<<
Or you could adjust the speed on your turntable for the easy fix - alternatively you can start / stop the track on the s2400 while adjusting the speed or buy the Octatrack that already have this feature
Yes i can buy an Octatrack and sell my S2400, but no 
Ajusting the turntable first is not an option because people will hear the pitch change, and you don’t want to disturb listeners.
I believe tap tempo is a great feature but does the S2400 average a number of taps before deciding what is the current tempo ?
Yes! There was a setting for the number of taps to average somewhere.