Spine scoliometer.
https://s3-us-west-1.amazonaws.com/h...e_fullsize.jpg
Previously:
https://www.homemadetools.net/forum/...860#post152540
https://www.homemadetools.net/forum/...554#post197267
Printable View
Looks identical to the sort of gauge I've seen used to measure roll angle on a ship...
https://www.amazon.com/Sun-Company-2.../dp/B00042K694
The tool no one wants to have to use.