To solve the black safe, you need to take all the wooden rings from the previous safes, and put them in the wooden puzzle board. Once on the board, they can be rotated individually to match with each other and the board. when done correctly, across the centre it will read: μ ε σ α . This can be translated using the calendar found in the yellow safe, which shows μ = 4, ε = 6, σ = 9, α = 1. So the combination for the black safe is: 4691