0:00 intro, 1:17 parts explained, 3:42 mounting options, 7:44 code change, 10:23 locked in forbidden zone, 13:34 totally messed up in forbidden zone.
Mechanical Safe Combination Locks have a forbidden zone. In this zone you cannot choose the last number - otherwise the lock will bind. Why this is and how this relates the correct mounting for the bolt orientation is subject of this video.