Agreed.

Some ships may be measured with main and tail wheels on the ground, but need a level on the tail boom (with spacers) and THEN measure weights.

Not sure?
Contact those that know, discuss with your local A&P.

Many ways to set up the fuselage, some may measure off structure (spar, wing leading edge, etc.) for data points, some measure "out in space"...,,,,
Read and understand, otherwise, ask a LOT of questions.