Measuring Inside Dimensions with a Tape Measure

[Toolmaker51]

I like all these solutions, commercial EZ Measuring sticks, the ancient pinch rod, and clamping scales together. The big advantage to Mr. Sparber's device is far greater range, limited only by length of tape measure.
Note; not all tape measure cases are such an easily figured size...

P.S. per your note in post *8. The photo + description of calibrating vs a flat scale makes this all the more worthy. Having an estimated dozen tapes makes adjustable compensation most sensible.

Why so many? I like them magnetic tipped for metalworking, laying out spaces for equipment, wiring, furniture, makes a centering tape ultra handy, the little 12'ers are distributed in vehicles and backpack for haunting surplus yards (imperial & metric in one!), extra-wide tapes for high upright measure needing a lot of tape rigidity, one each on various saws.....not to mention folding rules - engineers in 1/10ths, mason's, carpentry (with the slider).