This is how to pick a Master combination lock (604DAU).

With this lock, there are four "gates" per disc (wheel) where the lock will "click" when turned to the correct number (under tension).

For example, if you turn the first disc (under tension) (I tend to start at the disc nearest the shackle) and it clicks at 0 (zero), then the four gates will be 0, 2.5, 5 & 7.5 (ie this is 10 / 4 = 2.5 ... all the gates are an equal distance away from each other, at a distance of 2.5). You should get a click at each of the four gates, but sometimes it's difficult to tell luckily we only need one definite click to instantly know the 4 gates! We can ignore the gates are aren't whole numbers, so in this example, the gates we're interested in are 0 & 5. One of them will be a false gate (incorrect number) and the other will be the true gate (the correct number). You can often tell which of the two is the true gate, as it will often be "wigglier" under tension ... so in this example, turn to 0 and see how wiggly it is under tension (ie how much it rolls to & from the numbers next to it how "loose" it is), and compare with the wiggliness of 5. Choose the one with the most wiggle. If unsure, choose one of the two and move onto the next disc and come back it after doing the other discs (to again test the "wiggliness").

If the next disc clicks at (for example) 8.5, then you instantly know the four gates are 8.5, 1, 3.5 & 6 ... ie either 1 or 6 ... test for the wiggliest one and move on.

This will quickly open this type of lock (model 604DAU) but probably wont work for other types of combination locks.