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.

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