This video shows how a combination lock works according to the patent:
https://patents.google.com/patent/US3894415A/en
Correction:
When changing the code, first press the shackle down, then enter the current correct code. After that, push the shackle down further and only then set your new code.
If you skip this step, the drivers will disengage the tumblers in the wrong position, and the lock will not reset properly.
