and number two is look at the whells from above and as your turning them look for a little groove on on of the numbers on each wheel, there is a video on it somewhere but i cant seem to find it, i'll keep looking.
I did this once when I was a little kid. If there are only 3 wheels you'd be surprised how fast you can find the combo just be trying 000, 001, 002 etc all the way to 999. I got it open in less than five minutes, give it a try.