Boil off in unmarked kettle

I have no issue with anything in your comment.
Whatever works for any individual. In my case, it has hardly been anything resembling trial and error. But in the early stages 40+ years ago, when good information was somewhat more scarce and it was trial and error, I think I definitely learned more about brewing (and repeatability of results) than I would have otherwise.
Just sayin.
Like you, I had plenty of successes working that way while making very good beer, but I probably learned far more from my comparatively few outright failures (that's where the good note-taking helps...and teaches).
Cheers!

 

As a variation on marking a ruler/stick/spoon with markings that one must look at when the ruler/stick/spoon is touching the bottom of the kettle, I have marked my long-handled stainless brewing spoon with marks such that when the end of the spoon is at the surface of the wort (at the inside edge of the pot), the mark indicating wort volume is coincident with the top edge of the pot.

So my procedure is to simply have the bottom the spoon at the surface of the wort, and then place a binder clip on the spoon such that the edge of the binder clip is at the top edge of the pot. I then remove the spoon to see where the edge of binder clip is, reading off wort volume.

Cheers!

 

I use a metal yardstick and measure from a reference mark ( handle rivet) down to the top of the liquid. I filled with water a gallon at a time then a quart at a time after 2 gallons and recorded the measurement at each volume. Heated wort will expand but I'm not that anal.