This is a pretty good method, but sometimes it won't work. I've cracked several master locks in my life, and I found one for which the above method did not work--I kept getting the wrong 3rd digit, no matter how carefully I looked for the .5's. (Trying several hundred combinations in the process.) I recall another occasion when I gave up after finding two wrong 3rd digits (and trying 200 combinations), and another when my friend told me that the 3rd digit I found was wrong. With Google, I found this method, and it seems to work perfectly:
http://www.angelfire.com/ma4/masterlockcrack/3rd-2.html
It gives the same answers as the first method most of the time. Think about it: if the centers of the ranges of the lock are in fact arranged in a group of four xx.5's (e.g. 2.5, 12.5, 22.5, 32.5), a group of four xx.0's, and a group of three xx.5's and an xx.0, which is what the first method predicts, then the second method should give the same 3rd digit.
I know nothing about the internal workings of the master lock, so I can't argue for either method on its own merits, but I do know this:
1. Using the first method, I've failed at least three times, and I don't think I suck at implementing it. Using the second method, I have not failed yet.
2. On that lock for which I, using the first method, failed to find the correct 3rd digit after about five tries, I found the correct 3rd digit with the second method on my first try. This digit was, in fact, one of the digits that I was quite sure was not correct according to the first method.
3. The second method is easier to do and to feel confident about. Instead of seeing what looks like a .25 and trying to decide whether I should call it a 0 or a .5, I just need to see whether this range is the same as that range and these other two ranges.
It gives the same answers as the first method most of the time. Think about it: if the centers of the ranges of the lock are in fact arranged in a group of four xx.5's (e.g. 2.5, 12.5, 22.5, 32.5), a group of four xx.0's, and a group of three xx.5's and an xx.0, which is what the first method predicts, then the second method should give the same 3rd digit.
I know nothing about the internal workings of the master lock, so I can't argue for either method on its own merits, but I do know this:
1. Using the first method, I've failed at least three times, and I don't think I suck at implementing it. Using the second method, I have not failed yet.
2. On that lock for which I, using the first method, failed to find the correct 3rd digit after about five tries, I found the correct 3rd digit with the second method on my first try. This digit was, in fact, one of the digits that I was quite sure was not correct according to the first method.
3. The second method is easier to do and to feel confident about. Instead of seeing what looks like a .25 and trying to decide whether I should call it a 0 or a .5, I just need to see whether this range is the same as that range and these other two ranges.