When I first read about the troubles with bed leveling, I figured some inexpensive pressure sensors and an arduino would be an easy accessory. I found something "way back then" that would take well to clip on the edge of the plate and be compressed between the bed and plate and display either arbitrary values or difference between sensors. These things were tiny and now have become lost. If/when I get mine up and running, I'll probably pursue that option. It would be easier than sticking calibrated spacers at each corner and using objective feel by sliding a slip of paper between the plate and spacers. I think someone else suggested dial indicators and that might be easier too. Horrible Freight sells fifteen dollar indicators. Four of them and some 3d printed stands to hold them vertical might do the trick, although it would be important to calibrate the indicator bases to ensure they were all alike. I have a mini-mill and may build aluminum indicator stands for more consistent measurements, but that's for later.

What happens if one tries to use a non-FSL resin in the vat? It's not like there's a registration number embedded in the liquid or that one has to enter such information into the panel.