jasoncw
The reason you disconnect the WD hitch bars to get an accurate tongue weight, is because the bars transfer some of tongue weight to the front axle and back to the TT axle.
The weight of the TV only, subtracted from the weight of the TV with the TT on the ball without the bars installed, is the TT tongue weight.
I find the more useful information is the weight on the front, rear, and TT axle with the bars adjusted for a level TV and TT. This gives the total TV weight, axle loads, and cargo weight when compared to the weight of the empty TV.
However, some towing problems are related tongue weight so knowing how to determine it is handy also.