How to calculate the Square Root of any number using a 60+ year old method. My father was taught this when he was learning to be a plumber back in the 1960's. This was long before handheld calculators were around. It is needed to calculate the of the Hypotenuse of a right angle triangle so you know your work is 90° from your previous work. The only other way was to use the 3,4,5 triangle where 5=3+4.