How to figure out the combination for a Master Lock
Do you have a locked Master Lock and forgot the combination?
I'm going to tell you how to figure out the combination for most newer Master Locks with the keyhole in the back. This method will take about 20 minutes, so hopefully this information is not useful for anyone looking to take a lock that isn't their own. This lock cracking method will not break the lock and it will allow you to figure out the full 3 number combination so you can re-use the lock again.
Figure out the "catch" numbers
First, you want to close (if it isn't already) and spin the lock clockwise for half a dozen turns or so just to reset all the pins. Stop at the number 0. Pull on the handle. It shouldn't release (if it does, your lock is broken), but it should come out a little bit. You'll need to hold the lock in this position with the handle pull out as far as it can go.
Have a pen and paper handy.
Slowly spin the lock counter clockwise. You'll notice it catches at a number between 0 and 5. Write down the number. Keep doing this the entire way around. If it stops in between two numbers, write down a half number. For instance, if it's stuck between 15 and 16, write down 15.5. Some of the numbers will be whole numbers, while others will be between whole numbers.
By the time you get back to 0, you should have a total of twelve numbers written down on your piece of paper. Five of them should be whole numbers, while seven of them are half numbers.
Take a look at your whole numbers. Four of them should end in the same digit (like 8, 18, 28, 38). One will not end in that digit. Circle that number. That is the third number in your combination.
Time for some simple math
Take the number that you just circled as the third number in your combination and divide it by 4. It might not divide evenly. Remember in 3rd grade when you were learning fractions and your teacher was saying something about a remainder and you were daydreaming about that pretty girl who sat in front of you? Well, you need that remainder stuff now. After you've divided your third number by 4, what is the remainder? Just to give you an example, if your third combo number is 22, your remainder is 2 (4 fits into 22 5 times with a remainder of 2).
Take your remainder and write it down. This number will be 0, 1, 2, or 3. Now keep adding 4 to it until you reach 39. For instance, if your remainder was 2 your number list will be 2, 6, 10, 14, 18, 22, 26, 30, 34, 38. This series of 10 numbers will be the possible numbers for your first combination number. Write that down next to them.
Now, take the remainder that you used before and convert it to another number using this method: 0 becomes 2, 1 becomes 3, 2 becomes 0, and 3 becomes 1. Take that number and write it down. Now do the same thing we did before by adding 4 to your number up until 39. For the example that I've been using, 2 becomes 0 so my numbers are 0, 4, 8, 12, 16, 20, 24, 28, 32, 36. These are the possible numbers for the second number in your combination.
Putting it all together
Now you've got ten numbers that could be your first number, ten numbers that could be your second number, and only one number that can be your third number. That's a total of 10x10x1= 100 combinations. That's a big improvement over the tens of thousands of possible combinations without using this method. Remember that to use a combination you want to spin clockwise a bunch of times and then start on your first number, spin counter-clockwise past your second number one time and then around again and stop on it the second time, and then back clockwise to the third number and then pull the handle.