OK, I don't know if this will make it simpler or more complicated, but this is what I did:
Gave the girl at the local quarry a donation to the Cancer Society...per her request. No problems with that.
The quarry has a single scale, not for multiple axles.
With no TM hooked up, weighed just the front axle of the truck, then both axles, then just the rear axle.
Went home and hooked up the TM. Again weighed the front axle of the TV, both axles of the truck, all 3 axles on the scales, and then just the TM axle.
Front TV axle: 1st weight minus 2nd equals front axle unloading.
Rear TV axle: 2nd weight minus 1st equals rear axle loading.
Tongue weight: 2nd weight minus 1st of the TV only (both axles) equals tongue weight.
Total TM weight: Total of all 3 axles on the scales from the 2nd weigh-in, minus the total of the truck from the 1st weights. That should also equal the tongue weight (calculated above) plus the axle only of the TM from the 2nd weigh-in. OK, that sound confusing to me, even though I wrote it.
I did all of this several more times to determine the best position for my WDH.
The quarry here has a big digital readout that you can see at the end of the scales. I just made a chart, and plugged in the figures from the seat of the truck when the readout settled down. When reading the TM axle weights, I did have to get out of the truck (staying on the scales) and walk back a couple of feet because I was too far forward to take the reading.
The quarry scales have 20 lb. increments.
The worst part of all of this was waiting for a slack time in between dump trucks.
Hope this helps.
Chap