Mechanical calculators that are programmable? Well... not exactly. Charles Babbage almost succeeded building one in the mid-19th century, but the models I have are far less sophisticated than his invention. Even so... a decent slide rule is "almost" programmable. Algorithms exist to perform complex computations on a CURTA. Need I say more?

- Model Type Display Programming model Programming features Memory Special functions
CURTA II Curta II Stepped drum 15+8 digits N/A N/A N/A N/A
FACIT C1-13 FACIT C1-13 Stepped drum 13+8 digits N/A N/A N/A N/A
Keuffel & Esser 68 1210 "Log Log Duplex Decitrig" Keuffel & Esser 68 1210 "Log Log Duplex Decitrig" Slide rule 12" N/A N/A N/A N/A
Scientific Publishing Company's "slide rule watch" Scientific Publishing Company's "slide rule watch" Slide rule 2½" N/A N/A N/A N/A