The counters referred to in that context are basic 12v coin counters, but they're used to track credits in and out of gambling machines. Since location owners typically pay out of the till, those meter numbers are used to track how much goes in and out of the games so they can be set tighter or looser. Nowadays operators will have a printer system, as well as use machines that keep track of this in software. But the hard meters are a good backup.