It was circa 1930 and with 12 pounds of steel you could… make additions and keep a trace of your accounting! This Remington Rand (M175767) is a low-cost version. As you may see on the keyboard, the partial sum and the repeat keys are omitted by the manufacturer. The adder is relatively simple to operate. Simply key in the operands, and crank the lever once after entering each of them.
Repeat the operation for every number to add. The machine has a mechanical register that adds up the values automatically. When you want the read-out of the register – the total –, cranks the lever once (without entering any number), then press the TOTAL key and crank once again. Et voilà! Your sum is printed, with a nice trailing star character. The register has an overflow, and the position of the clear level (on the front of the adder) tells you how far you are from overflow. Indeed, at each keystroke, the lever shifts toward the left. You can also clear the register by pulling the very same lever to the right. Subtractions are possible by using the 9 complement method. What is really mad, is the all this is pure mechanics, no electronics involved whatsoever.