personally I use a Sherline Trailer Tongue Weight Scale - Sherline Products don't remember, but I think I have the 5,000lbs one. Easy enough to change... 1 square inch piston just means putting in a different size pressure gauge & pressure = weight 1 to 1. Probably more effort to use, but much more portable & adaptable to other junk.
I use the Sherline also, along with Weigh-Safe Trailer Hitches - Towing Peace of Mind in the 2.5" shank model when setting up a new trailer. Both models approximately agree with each other on the tested tongue weights.