The job: a record of who actually turned up
How it is done today
Most studios take attendance in one of three ways: a clipboard by the door, a trainer counting heads, or nothing at all. All three produce the same result at the end of the quarter, which is a conversation about whether the six o'clock class is working, conducted entirely from memory and preference.
A logger changes that conversation by making it about a record. It also does something more immediately useful: it shows which individual members have stopped attending, which is the only early warning a fitness business gets before a membership quietly ends.