Boom Pole Perceived Weight Calculator
For the "Fulcrum" distance it's how far into the boom pole do your hand hold. In the image below your hand would be on the end of the boom pole pulling down and then the fulcrum is your other hand holding up the load which in our case in the microphone.
So if the line below was 2 meters total from left to right then the Fulcrum distance which is half way would be 1 meter.