The article linked to below describes how to pick a combination lock made by master lock. The technique takes a little time to master, but once you do it a couple times, you can crack a master combination lock in under five minutes. The nice thing about this lock picking technique is that it does not require you to alter the lock, so you can use it to pick the combination lock and re-lock it when you are done so that nobody even knows that the lock was opened. You can also use this technique to recover the combination to a master lock that you own.