[Denny_A]

.....did, then never paid attention again.

With my 4Runner sitting level and UNLOADED and filled with fuel, I measured the front/rear height at selected, easily identifiable points - my baseline reference.

Plugged my WDH hitch into the receiver, then measured the new F/R heights. After that I started piling weights on the hitch and measuring new height F/R at each 50 lb interval. After having added 600 lbs (free weight discs) I had a table of the effect of load on the hitch.

I then plotted an an x-y graph of Front height change vs. weight and Rear height change to weight.

When actually loading the vehicle with the trailer tongue (no cargo or pax), I then had a handle on tongue weight without actually weighing the tongue.
We usually loaded our trailer the same way for travel, so I also had a good idea of the effect of cargo and pax as measured at the hitch. I.e., If the cargo is loded in the TV for travel, and the trailer tongue is on the hitch as dead weight, the change if F/R heights indicated the combined effect on the hitch. Add a couple of pax up front (using free weight equivalents), I could use the combo-graph to come up with a number.

Typically one shoots for the front measurement CHANGE to be equal to the rear height change or less than (by up to 1/2 inch) the rear height change. Within that range the cargo plus pax effect was nil. But, I wasn't loading 200+ lbs of cargo behind the axle.

So, from then on I dropped x-links and measured F/R height change within 1/2 inch whilst ensuring the front NEVER dropped more than the rear!

For my 2720SL, 750# spring bars were just right!