I learned this trick many years ago, and it definitely works. A friend of mine had an old lock he didn't remember the combination to, and within five minutes I had it opened and the combination written down for him thanks to this trick.

To see how combination locks work, see http://woodgears.ca/combolock/index.html. The video at the end of the page is particularly helpful.

Did anyone try it? I don't have a master lock on hand.

I found a Master lock that I know the combo to (I consciously tried to not let knowing the combo influence the "where are the clicks" results).

Got 12 candidates and seven .5 numbers, just like it said. One of them was the correct last number. Throwing away the .5 numbers left four numbers with the same digit in the ones place and an odd man out which was indeed the correct last number.

The modulus trick produced the correct first number in the resulting candidate list and the second number candidate list contains the second number. So yeah, does work on this lock (where "work" == the method results in only 100 combinations to try manually, one of which I know is correct).

I live in an apartment building and in the basement we have storage lockers. Someone had a master lock on one, so I tried it out. I was losing confidence by try 95 (out of 100) - but it opened on try 96! Pretty cool.

I never knew about this trick. The only one I know is how to pop the lock open and then reset the code.

This is really cool though.