Two video guides to mechanical three wheel combination safe locks. The one shown is a Sargent and Greenleaf 6730 with small dial on a Churchill Extra under floor safe. The first clip just shows good dialling system which will work well with any chosen numbers. The second video shows the procedure to change the numbers of your combination. Code change for three wheel safe lock, please avoid the “Forbidden Zone” for the last number in sequence. Where the dial stops when the lock is open should be somewhere in the 90s making the forbidden zone between zero and twenty. If dial stops elsewhere then call a safe engineer when it’s time for a code change! Chubb dials had a blank area between 100 and 0 which is the forbidden zone so all other numbers can be used. Please make consecutive numbers at least five digits apart, 30, 40, 31 is fine but 30, 31, 40 may cause dialling issues. Try to avoid ascending or descending sequences like 20, 40, 60 or 90, 80, 70 go for 20, 90, 40 and better still set at least one of the numbers away from a ten or five. For the highest security don’t chose a combination that could be guessed using easily found info such as a family birthday. You will need the correct changing key to suit the specific make and model of lock. S&G, La Gard, Mosler, Diebold, JIS, Ilco, M-locks often there is an envelope with change key and instructions kept inside a safe. If not then better to call a local safe engineer to check and service safe and help with code change then they can supply the correct key and instructions for the next time.