From Oregon OSHA – about as easy as can be used. Takes into account starting position, repetition, amount of time per day, twisting. Laughably easy, anyone can use this one.
Click link below for directions to app:
https://itunes.apple.com/us/app/safe-lifting-calculator/id794013425 – From your computer.
https://appsto.re/us/X76uV.i – From your iDevice