The Friden Calculator (1934) was the most advanced mechanical calculator ever manufactured. Its crowning achievement was fully automatic square root extraction — a feat no other purely mechanical calculator could match.
The square root mechanism worked by a systematic trial-subtraction method: it would automatically cycle through subtraction attempts, counting successful subtractions, and shifting the carriage — all without operator intervention. The entire process was purely mechanical, accomplished with gears, cams, and levers.