TabulatorI found an old adding machine at a local thrift store, and thought it would be a really cool thing to have.  For a couple of bucks, I didn't expect it to work, and when I first tried it it was almost completely non-functional.  So little of it worked that I couldn't even figure out how it was supposed to work.  In particular, I'd seen references to clearing the machine before beginning a calculation, but none of the keys seemed to do anything close to resetting it to all zeros.

So, I began to take it apart to figure out what might be wrong with it.

Housing removed
Housing removed  This turned out to be a bit of a problem, because the paper advance mechanism needed to be removed before the outer case could come off, but there was no obvious way to remove it.  I had almost completly disassembled it before I figured out that it was designed for easy removal, and simply slid off sideways.  It took a long time to get back together again.

Lots of WD-40 later and much of the machine was working.  The units column continued to be a problem.  I found a bent rod in the units column mechanism and straightened it.  It was probably caused by forcing when the machine was jammed.  Even this did not fix the problem, though.

I pulled the keypad and the display wheels.

Far inside
Far inside  I found out lots about how the thing works, but I couldn't see anything amiss in the units column.  I finally noticed that the rod I'd straightened was meeting another rod at a slight angle.  When I more carefully straightened the rod again, the binding I had felt at that joint went away, and the units column started working properly.

Fully assembled, the machine is now fully functional once again!