I was "between gyms" for about a year. When I joined my current gym, I realized that I had completely forgotten the combination to my lock. I tried a few sequences, but couldn't recall the correct one. So rather than leave my stuff in the locker unlocked (you know there's a black market for white dress shirts, right?) I bought a new lock from the gym. As I was working out, I repeated the new combination to myself over and over, imprinting it on my brain. Then it occurred to me: I already knew this combination.
I went back to my locker, got out the old lock, tried the combination, and CLICK, it opened. My brand-new lock had exactly the same combination as my three year-old lock! I thought, what are the odds!? Then I thought, what are the odds?
The first and easiest answer may be 1-in-64,000. The combination has three numbers, each ranging zero to forty, so 64,000 is what I assumed initially. This made me feel very lucky. (Lucky doesn't seem like the right word...coincidence-stricken?) As nice as it would be to feel so luck-- er, coincidence-stricken -- I had a hunch there was more to it.
Both locks were manufactured by Master Locks, so I thought that perhaps the people at Master Locks must be so lazy that they actually only use ten different combinations in all of the locks that they sell! I like that theory, but I admit it's unlikely. So I went to the internet to put an end to the mystery once and for all, and what I found was nearly as shocking as the Lazy Master Lock Theory.
I won't bore you with the details. I'll let this guy bore you with the details, and I'll summarize: Because of the way they are made, there are only 100 possible correct sequences to single-dial combination locks. Think about that the next time you protect something valuable with one of these "locks".