The CURTA calculator

The CURTA calculator was the most accurate calculator that didn't use electricity, first conceived by Curt Herzstark in the 1930s, and by 1938 Curt had filed a key patent. The same year, the Nazis had Anschlussed Austria and forced him and his company to make precision instruments for the Wehrmacht. War is the only thing going through their minds, huh? In 1943, he was taken to a concentration camp, Buchenwald, where he was encouraged to continue his research.

He was able to develop working drawing for the device. Thankfully, Buchenwald was liberated by U.S. troops on April 11, 1945.

While the output display on mine is limited to 15 (The white part of the digit counter counts how many revolutions the crank has gone through), you can still think of neat tricks to make it go above a hundred trillion.

When writing, say,

999,999,999,999,999,999 X 999,999,999,999,999,999

What I've found works best it to just multiply the largest numbers first (999 x 999 = 998001), account for the additional zeros, then continue until you have each number, then add it. I'm sure there's a faster way, but it sure is better than doing it 100% by hand.

Here's a very good video explaining it: https://www.youtube.com/watch?v=qyrY6uss-04