It looks like they used 7 bits per decimal number (going clockwise, with red=1, yellow=0). With 7 bits, you can represent 2^7 decimal numbers:

0000000 = 0
0000001 = 1
0000010 = 2
0000011 = 3
0000100 = 4
...
1110110 = 118
...
1111111 = 255