I'd consider both abacus and a mechanical cash register (or even mechanical arithmometer) as digital/discrete devices, not analog; analog calculation would refer to slide rules, nomograms and the like (of which I'm sure there would be more than the slide rules and nomograms, but nothing comes to mind..).

Yeah, on thinking about it, seems like you're right.

Too bad, I can no longer think of any then. I think ballistic computers were at one point analog, but those should all be obsoleted now.