in the example above, the top half values are 2,6,1,1,4,5,1,2. this sums to 22 = 6×3 + 4. thus the check symbol has a top value of 4. the bottom half values are 6,4,2,2,4,0,2,5, which sum to 25 = 6×4 + 1. the check symbol's bottom half value is 1, so it corresponds to the letter i.