Calibrating a measuring stick?

[BenB]

Well that's advantage of using a carpenters square. You drop the ruler bit down until it hits the surface and begins to form a meniscus and then lock the screw and read off the result. No parallax error either because you can remove the carpenters square to make the reading. I've made up a simple java webpage which is hosted on my NAS which converts readings at different temperatures to volume (calibrated for my pot). It's quick and simple...