Let's say the "real" load on the ball is 1000# with no cargo load on the rear of the TT, and
let's say the "real" load changes to 900# when cargo is added.
Let's say a scale with 2000# capacity and accuracy of 2% of full scale (40#) is used to provide an indication of these real loads.
The "indicated" load with no cargo might be 960# or 1040#, or it might be 1000#.
The "indicated" load with cargo at the rear of the TT might be 860# or 940#, or it might be 900#.
If you're interested in the amount of "tongue weight reduction", the calculated difference between the "no added cargo" indicated load and the "added cargo" indicated load might be as low as 960-940 = 20# or as high as 1040-860 = 180#.
The scales readings could give errors of +/- 80% versus the "real" difference of 100#.
OTOH, they might be accurate to within a few pounds -- but how are you going to know?
Seems to me you might as well use an estimate based on a formula.
Ron
