When measuring a distance with a 100 foot steel tape supported at both ends the sag formula needs to be applied to correct the distance. Does anybody know why an overall distance does not work in this sag formula? For example If you measure a distance of 735 feet you would have to apply the formula eight times once for each set of measurements. Seven for 100 feet and once for 35 feet and add the eight results. Why does the formula not work if you enter 735 feet?

Cs = (-w squared) (L cubed) / 24 (P squared)

Cs = correction for sag

w = weight per unit length of the tape (pounds per foot)

l = length of the suspended section of tape in feet

P= tension applied to the tape