Cracking a Master Combination Lock
This is the fastest way to crack a Master Combination Lock of the style shown. I don't know how it works for newer models. You don't need to write anything down. All you need is the ability to add 4 or 2 to a number and the ability to hold 3 numbers in your head at once. Using this technique you can narrow down the number of possible combinations to 90. A further trick exploits the function of the tumbler mechanism to allow you to rapidly try sets of 9 combinations in quick succession without having to reset the first number every time. It takes 5 minutes on average, and at most 10 minutes, to crack the combination.