As one truckers website I found says, they are RFA (really f'g accurate).
I once took our truck and TT to 3 different scales on the same day - a grain elevator and 2 commercial truck highway scales. All agreed within 20 lbs. Another time I used a CAT scale and commercial hwy truck scale on the same day and same thing - within 20 lbs. That is RFA! ;)
Where I have found inaccuracy is between the factory UVW and scale weight immediately after picking up our new TT from the dealer - 190 lbs heavier (after factoring in propane tanks and battery). No idea why the difference.
Everything you want to know about scale accuracy and weighing RVs here on
Fifth Wheel St.edit: I see someone already posted the link to FW St.