It's actually the last number. It's found by pulling the shackle and noting where the dial sticks. There will be several places but one stands out from the rest

It's actually the last number. It's found by pulling the shackle and noting where the dial sticks. There will be several places but one stands out from the rest and is the last number. Then the last number mod 4 is equal to the first number mod 4 while the middle number mod 4 is ± 2 from the others. This reduces the search space to 100 possibilities to be brute forced in a few minutes.