To avoid trying to hold a ruler or tape measure steady in just the right place - and not yet having the experience to tune only by eye n intuition! - I've created this 3d-printable gizzmo for more easily making repeatable rig measurements:

• On circular booms ~5-11mm dia., for measuring foot depth (e.g. IOM/DF95/DF65). 

• Against the mast, to measure gap to jib boom ("3 fingers" is a subjective measurement!)

• Against the backstay, to measure leech twist.

• Measurements can be taken between inside-edge(s) if you prefer, or the V underside allows for measuring from the centreline regardless of spar diameter. (Just add/subtract radius if necessary). 

Happy to hear any ideas for improvements.
A variation to sit on SAILSetc rectangular boom could certainly be done - the relative dimensions just don't allow a one-fits-all.

The g-code file is offered for free, but please don't make/sell for profit. If you find it useful then a modest donation to https://prostatecanceruk.org/ would be kind.

Edited February 27Feb 27 by Colin Helliwell

Would you be able to offer to print for cost plus donation as I would like one of these but no printer?

Version 2