What I rode yesterday, 1962 Continental with 1962 VDO "Fahrrad-Uhr" ("Monitre velo"):
Another favorite of mine is this "Peugeot Sport Computer" on my 1979 Super-Sport.
It's got 4 functions, plus scan mode, and has a full 5-second response time to keyboard input.
Fellow riders of the local peloton call it "the laptop".
It's AA-powered and I see still showing the mileage from my trip up to Nevada City last October.