detents
Babbage was not a fan of springs, which at the time were not uniform and were prone to failure. One of his 1837 "Principles of the Engine" was "to have no springs to do work, only retaining springs". But he certainly made liberal use of spring for detents, which impose one or more preferred locations for an otherwise continuous movement. It is, as Tim Robinson observes, a "soft" version of the locking that he uses when parts should not be moving at all. Here are examples, some of which include the option of a hard lock. So how to easily implement detents, with fewer parts -- and in particular fewer vertical shafts? My first attempt was to use a "spring plunger" from McMaster-Carr, which is an acetal plastic nose in a steel 8-32 threaded case, with an embedded spring that provides 1 to 3 pounds of force. I used it screwed into a 3/8" vertical shaft and had it engage with notches of the kind Babbage showed. It works, but the small 1.7mm tip si