With four sets of digits, opening this lock has approximately 10,000 possible combinations. Actually, it has EXACTLY 10,000 possible combinations.
Fortunately, these locks have a very simple, intuitive lock mechanism. The next step will briefly describe the mechanism, and subsequent steps will show you how to actually reclaim the combination, meanwhile opening the lock as well.
Disclaimer: Don't steal people's things.
Step 1: Inner Mechanical Workings (FYI)
Imagine a Master combination lock as simply a a number of discs (or rotating dials) with notches in their inner circumference. These notches correspond to a particular number on the outside of the disc (the part we use to unlock it). When the correct number sequence is inputed, the notches line up, and the bolt is released.
The most important things to know are (1) all 4 numbers must be correct to release the bolt (2) as we can't see the notches, we have to rely on touch to feel when a notch is engaged or not, (3) in order to feel when a notch is engaged, we need to provide upward pressure to the bolt, and (4) in order to feel each number out correctly, we must start from the bottom up as this will allow us to know when each subsequent notch (up the lock towards the bolt) are engaged.
Enough of this. Lets pop a lock.
Step 2: How to Feel Out the Lock
2. Now curl your ring finger into the U-shaped space the bolt makes, and provide steady pressure, pulling the bolt outward from the lock. If you can find a more comfortable position to hold the lock steady and provide upward pressure to the bolt, then high-five.
3. Once steady pressure is provided, then begin with the lowest disc (towards the bottom of the lock) and turn it counter-clockwise slowly. You should feel some tension in turning the disc. Thats exactly what we're looking for.
4. At some point while turning it slowly, you'll find the resistance to turning will go away. That means the notch is lined up correctly and therefore not engaging the bolt. It might happen very quickly, so as soon as it does, stop turning and take note of the number. That'll be the last number of the number sequence. Leave it at that number and continue on.
5. Now work your way up doing this to every disc. The last disc will be very easy to complete, if you've done it all correctly, as it will be the only notch still engaged with the bolt and the pressure will be very easy to recognize.
6. In order to find the combination of an unlocked Master lock, simply go backwards, providing pressure down onto the bolt and working down the number dials rather than up.