I looked and it seemed quite complicated with things called arms and datum I've never heard of before in reference to aircraft. One pictured showed a calculus formula after weighing the three wheels. Plans already indicate location of CG. I was interested in finding out how people usually do this. The scale idea would work if I understood the concept, though I only have one scale. The other option would be easier, but I'm a little concerned about 1/8 plywood holding full weight of the aircraft.