How to keep score with coin at rails when playing bank by the rail to 100

[brucehillchicago]

I see Billy Thorpe and Mike Delawder doing this and don’t understand how it works .
Can anyone explain????
The one coin moves clockwise then backwards when the other player shoots and scores.
There are only 18 diamonds on a table so how do they keep score if playing to 100 rails????
Thank you

 

[skogstokig]

next after 18 comes 19... so that part shouldn't be insurmountable

 

[Bob Jewett]

next after 18 comes 19... so that part shouldn't be insurmountable

I'd use a penny and a dime for each player so you only have to go to 9. Easy. Add a quarter to get to 1000.

 

[Bob Jewett]

As for how the players are doing it, I'll guess that they are keeping track of how many "laps" the coin has made. John Schmidt used to do this for 14.1. 420 points is 30 racks so one lap plus 12.