Your digit keystrokes position little dials to confirm what you entered, as well as a stack of thin, small cams, one stack per digit. This sets up the gear ratio that corresponds to the number. The accumulator comes out of the dip, the dials get over their shyness, and magically align to show the new sum, carries and all. If you think this is bad, division gets downright hairy. The snail cam followers are in contact, and as the dials rotate, the follower movements have really interesting consequences.
Division seems to be really complicated in detail.
It is so fast that you can serially enter the digits of the multiplier, and it gobbles them up like a starving Brontosaurus. I personally remember trying consecutive 9s, and finding that the delay was really minimal. The internal details when all is taken into account become formidable, especially in division. The full details seem somewhat less so, but the complexity and sophistication of the design are truly notable. There's hope of scanning the illustrations in the training manuals, doing a lot of cleanup, and publishing them with descriptions on Ernie's pages.