This tool tracks bets on the left and right sides of dozens:
1st dozen left: 1,2,3,4,5,6 | right: 7,8,9,10,11,12
2nd dozen left: 13,14,15,16,17,18 | right: 19,20,21,22,23,24
3rd dozen left: 25,26,27,28,29,30 | right: 31,32,33,34,35,36