I have a small collection of old electro-mechanical calculators from Friden and Monroe, and they are real beasts to lift and to operate. My Monroe calculator is fully automatic, in that it will do the repeated additions to perform multiplication, but boy is it noisy! I can’t imagine an office full of these machines all running at the same time. I was hoping to see Mad Men or some other TV show have some people using them and showing us how noisy offices were then, but they’re finicky so I imagine it’d be hard to get more than a couple working at the same time.
There are collectors of the old calculators and cash registers, but they’re surprisingly hard to find, especially the late models. I think everyone scrapped them for their metal content (about 40 pounds) as soon as electronic calculators were available.