Years ago I had a small, quite inexpensive, instrument specifically for measuring maximum rig loadings under actual sailing conditions (read in lb’s or maybe ft lbs I can’t remember back that far). It was a small gauge that I used to attach between the rigging wire and its anchor point either at the hull or at the hounds up the mast, and it would show the maximum loads that the rigging at that point had been subjected to. It had a graduated gauge and the reading would stay at the maximum that it had been subjected to. To use it again it was a simple press point reset back to zero. It was very interesting initially but as the max’ readings never ever approached the safe loadings given by the wire manufacturers, I stopped using it and like most unused things it has gravitated to that “unknown place” where all such similar things seem to disappear to.
I also used at that time a “pressure pad” that I would place under the base of the mast to show, similarly the maximum compression generated down the mast. I also stopped using that years ago as well. Actually from memory, unlike the loadings on the wire, which were quite disappointingly low, some of those mast compression loadings were quite horrendous.
We still regularly receive “industry” advertising literature offering for sale a whole range of suitable instruments for measuring every conceivable loading on every conceivable material in every conceivable position, the big difference “now” from “then” is that they all cost an “arm and a leg” to buy now. BUT THEY ARE ALL DIGITAL (which obviously makes them better and worth more, although they still only do the same job with no apparent greater accuracy if you can believe their data)