How the Method Works (page 2)

How we find the first and second numbers on the "old" locks:

he picture above shows a rear view of a disassembled lock without a case. The lock dial, upside down, is at the bottom. The 3 cams, shackle and latch assembly are visible. The notch on the back cam is lined up under the pawl. The notch on the middle cam is not lined up under the pawl, but is visible. Shallow notches on the front cam are visible.

Note that the cams have pegs on them. Only the peg on the rear of the back cam is visible in the picture above. However, the other pegs are just like it. (The peg on the rear of the back cam is like the other pegs, but does not drive a fourth cam. However, it has a function, described later.) As the front cam is turned, when a peg engages with the peg on the middle cam, that cam starts to turn. When the peg on the other side of the middle cam engages with the back cam, it also starts to turn. Thus, the process of turning the dial twice to the right ensures that all three cams are turning. When the dial stops at the correct first number, the notch on the back cam is lined up under the pawl. When the dial is turned left one turn, the back cam does not turn and its notch remains lined up. The peg on the front cam engages with the peg on the middle cam, and both turn. The middle cam's notch lines up under the pawl when the correct second number is reached. The dial is then turned right and the front cam notch lines up when the correct last number is reached. The three notches are lined up and the lock will open.

The simplified procedure leaves the back cam stationary while the possible positions of the front and middle cams are tried, thus avoiding the necessity of dialing all digits in the combination each time a new combination is tried with the same first number.

One of the hints is to notice the slight increase in effort needed to turn the dial when the dial reaches the number just tried as the second number. The dial becomes slightly harder to turn because the peg on the front cam engages with the peg on the middle cam, and extra force is required to push both cams.

To provide locks with all possible combinations, Master would need to use a much larger number of different cams. Not all 64,000 combinations are possible, due to mechanical constraints. However, it should be possible to make locks with 48,960 different combinations.

There are 2,560 possible combinations that follow the rules here. On its web site, Master claims to have 1,500 different combinations for the padlocks, so they must have reduced the number even further. It appears that Master reduced the number of combinations in order to reduce the number of different cams it would need to manufacture and stock. Using fewer cams would cut the manufacturing cost of the lock.

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