A borrowed ring is locked on a 4 digit combination brass lock and, the dials are mixed.
Spectator can test that the lock cannot be opened. Spectator thinks of a 4 digit number & dials them on the lock.
This proves to be the secret numbers that opens the lock!
Important points:
- Mechanical, nothing to break
- Nothing added or taken away
- Spectators set the chosen numbers on the lock!
