Things You'll Need
Master combination locks are used to secure lockers at school, work or the gym, as well as shed doors and equipment chests. If you forget the combination and can't find where you stored the information sheet that came with the lock, you have a couple of options. You can either send the lock to Master Lock and wait several weeks to get the lock and its combination back from the company, or you can figure it out with a bit of detective work.
Move the Master lock's numbered dial clockwise; spin the zero past the indicator arrow for three consecutive passes. On the fourth pass, leave the zero under the arrow. Pull the shackle clasp up, which will make the dial stick and somewhat difficult to move. While you pull the shackle clasp up, start moving the dial clockwise until it stops and won't spin around any further. The dial will stick at every three or four consecutive numbers before you won't be able to move it anymore. Take note of what number is under the arrow at this time.
Release the shackle clasp. Pull the shackle clasp back up and spin the dial counterclockwise until it stops. The distance from the first clockwise spin stopping point number to the second counterclockwise spin stopping point number is the range of the third number or last digit of your combination.
Write "third number range" down on the top line of your scrap paper. If the range is two consecutive numbers, record the number between them, which will be the lower of the two numbers with a 1/2 after it. For example, if the dial stops between 3 and 4, write down "3.5" or "3 1/2" on your scrap paper. If they are two numbers apart, let's say 16 and 18, record the middle number, which in this case is 17.
Let go of the shackle clasp to move past the stopping point of the dial. Spin the dial clockwise three times past zero and stop on the zero on your fourth spin. Find the clockwise spin stopping point and the counterclockwise spin stopping point range and write down the number. Repeat this process until your range of numbers has gone all the way around the dial to zero. You should have a list of 12 range numbers at this time.
Examine your list of 12 numbers. Write an X over any number that ends in a 0.5 or 1/2 as these numbers are not a part of your combination. Look at the remaining range numbers. Four of the numbers will end with the same number in their single digit or one's column. Write an X over these numbers as well as they are not a part of your combination. The remaining number is the third number of your combination. Write down "combination third number" and the number you just figured out through the process of elimination on the very top of your paper.
Write "second number range" on a new line below "third number range." Divide the third number by 4 and write down the remainder next to the possible first number. The remainder will be zero, one, two or three. Add 4 to the remainder number. Write this number down. Keep adding 4 and writing the number down until you go all the way around the numbers on the dial and reach zero.
Look at the possible second numbers and write an X over any of them that are plus two numbers away from the third combination number. Write an X over any that are minus two from the third number of the combination. The remaining number is the second number of your combination. Write "second combination number" at the top of the paper and write down the number you came up.
Determine the first number of your combination. This can be a little time consuming and tricky. Add 2 to the second number and write it down. Add 6 to the second number and write it down. Do not use these two numbers as you determine the first number of your combination.
Start going through the numbers on the dial, one number at a time, until you find the first number of your combination. Spin the dial clockwise twice past zero, enter the first number on the dial that is not two or six more than the second number, turn the dial counterclockwise past zero to the second number, and then turn it clockwise past zero to the third number.
Keep going consecutively through the numbers on the dial as you try to find the first number, remembering to avoid the numbers that are two or six more than the second number. When you determine the first number of the combination, write it down on the top of your paper next to "first combination number."
If you aren't confident in your math skills, you can always use a Master Lock combination calculator. Just type "Master lock combination calculator" into your preferred search engine to find one.