I'm a sucker for puzzles, especially when I can't figure them out. Someone could probably trap and kill me by using the human equivalent of the monkey trap if the trap consisted of something I couldn't figure out, but which looked as if it maybe could be.

I think that whether puzzles are a waste of time depends on whether they are enlightening or possibly entertaining. But you really "get" nothing, other than a vague and fleeting sense of accomplishment in having figured out something that someone put there for you to figure out. Perhaps I'm a twisted sort, but I get more pleasure out of solving the kind of puzzles that people really don't want me to solve. But I don't like to waste time spinning my wheels trying to solve things which can't be solved.

I say this because like the monkey with the monkey trap, I was unable to ignore a puzzle in the form of this ordinary Master Combination lock, which the previous occupants left in the basement.

It's your typical low security locker room type combination lock that most of us used at high school or college. While they can be hammered open or opened with a shim like this, without a combination the lock alone is useless absent a trip to a locksmith (who'd probably charge more money than it would cost to buy a new one).

A sensible person would probably have thrown it away, but I just couldn't resist temptation, and it ocurred to me that there might be information about how to crack the combination. Sure enough, there are innumerable sites and videos demonstrating in detail how to do it, but they seemed a bit hokey, and I was skeptical. Even if you follow the directions exactly, the whole thing requires patience. More patience than most people have. Factor in skepticism, and you find yourself wondering (as I did) "what if this is a complete and utter waste of time?"

Now, a combination lock marked from 0 through 39 with three combination numbers yields 64,000 combination permutations. Only an insane person or a savant would actually sit there and go through them all in the hope of opening the lock. But website after website (and video after video) claim that you can reduce the number of permutations to 100 -- provided that you first discover the crucial third (and final) number of the combination.

To my astonishment, I found that the third number can be found by the method demonstrated in this YouTube video,

What you need to do is summarized here (and described in detail in many other places):

First, we need to find the last number of the combination. To do this pull the "U" shaped thing away from the lock. It helps if its attached to something. (A Locker?). While pulling it out, start to rotate the dial from "0" so you know where to end later. You will notice that the lock will stick to a certain number. Now release the "U" for a second and then start to pull while you start to rotate again.

3) Next write down all the places the lock got stuck at while you were rotating it. There should be exactly 12 places if you did it right. One of these 12 numbers will be the last number of the combination.

4) Now we need to eliminate all of the numbers, but 1 to find the last. There are two types of places where the numbers you found got stuck at. First type is exactly on a number which means it won't move left or right while pulling up the "U". The second type is when the number you found was actually stuck between two numbers on the dial, and it would budge a little to the right or left.

5) Since we can determine, which of the 12 numbers were in between two numbers we can now eliminate them. There should have been 7 of those, which means there are only 5 left on you list.

6) Take a look at you list now and you should see that 4 of the 5 numbers left on you list have the same one's place digit. (ex: 05, 15, 25, 35) These 4 numbers you found are fake and should be eliminated. This last number you have left should be the last number of you combination.

7) To find out the Master Lock Combination is easy now that you have the last digit. You now have 10 first digit possibilities and 10 second digit possibilities. This means you have to try out a maximum of 100 combinations. And don't think that's too many because this is much better than having to deal with 64,000 combinations.

So that had to be it, right? I was still skeptical, though, and I was even more skeptical when I ran the number through this Master Lock Combination Calculator and saw a huge list of possibilities.

There's something about the thought of trying 100 different combinations when you're not convinced the whole thing isn't hokey that's a bit intimidating. Suppose you get to the end and it still hasn't opened? How would you know whether:

the Master Lock company changed its lock algorithm as the conspiracy theorists claim;

you didn't get the correct third number;

you make a mistake and didn't line up a number correctly, or passed one not enough or too many times; or

the whole thing is some sort of Internet viral hoax.

I cannot describe the inexplicable and irrational feeling of satisfaction when it opened. I actually felt as if I had accomplished something.

However, I wish I had taken to heart this commenter's advice:

Just cracked a newer 800xxxx serial lock using this method (and the combo calculator linked). Was 5th from the bottom of the list though. Maybe that was done on purpose? I would recommend starting from the end of the list and working up. Good luck!

Furthermore, because I had originally found the lock open, I really wish I had known about this!

There's a few more tricks to narrowing down the possibilities. One is if you find the lock open, hold the clasp in locked position and rotate the dial counterclockwise. The dial will catch, causing the clasp to rise, at (I believe) 6 numbers before the FIRST number in the combination. That will narrow the possibilities down to under 10. And, in my experience, the difference between the first and second number (and the second and third number) is always 6 or more. That'll help narrow down the possibilities by about a third.

Then there was this, which I have no way of verifying because I never had the "official" combination to this lock:

Also tried it with a lock I knew the combination on and I ended up with a completely different combination that still opened the lock. I wonder how many different combinations you can use on the same lock? I'm guessing several.

But alas! The problem with the theory that I "learned something" is that had I failed, I'm sure I would have "learned" some very different lessons....

MORE: I don't know why it took me so long to put two and two together, but I just realized that there is no need for anyone needing to figure out the combination for one of these locks to go through the 100 permutations as I did. All you need to do is the following, which I'll break down into two broad steps:

When you have the first and the third numbers, you'll be able to isolate one grouping of ten from the list generated by the Master Lock Combination Calculator, and you'll only need to try ten combinations.

Ten is easy!