jdfoils said..
Not at all difficult if you have a place with a level floor and two stands the same height (i use sawhorses with a v-block on top), i also use a gauge stick to measure spacing as it is easier to get an accurate measurement than using a tape
Mount the mast with the ends on the stands
Measure the length of the mast, calculate and mark the 25, 50, and 75% station locations.
Measure the spacing to the floor at the 25, 50, and 75% stations
Hang the weight
Measure the spacing to the floor at the 25, 50, and 75% stations
Rotate the mast 90deg
Measure the spacing to the floor at the 25, 50, and 75% stations
Hang the weight
Measure the spacing to the floor at the 25, 50, and 75% stations
Rotate the mast 90 deg
Measure the spacing to the floor at the 25, 50, and 75% stations
Hang the weight
Measure the spacing to the floor at the 25, 50, and 75% stations
Rotate the mast 90deg
Measure the spacing to the floor at the 25, 50, and 75% stations
Hang the weight
Measure the spacing to the floor at the 25, 50, and 75% stations
Calculate the deflections
Calculate the average, min, and max stiffness and bend %
Done, now move to your next mast
Variations between masts and in mast orientation are greater than the measurement accuracy; easy to verify using a gauge study
No floors are level. Previously I've used a string line or a leveled timber base. and like you each 90 deg turn provides different numbers. Used gear is note ideal..
I think you may also be inferring tolerances are all over the place. Surely that's a thing of the past. More advanced building techniques are more accurate. I know of a couple of brands that changed fabricators back in the day because tolerances were out of spec. They check random masts.