How many know their actual pin weight. Serious 5vr's should. Most discussion regarding trucks are more about towing capacity, when it needs to be about pin weight which is the biggest part of cargo ...
Do not recommend unhitching a trailer on the scales. You are tying up the scales for a fairly long time and there may be others wanting to use the scale.
It is simple. Move to an area out of the way then unhitch the trailer and go back to the scales and weight the truck.
Pin weight is the weight difference of both truck axles with the trailer hitched and the weight of both ruck axles without the trailer.
Using only rear truck axle weights will not give the true pin weight.