first placed the pot on a level surface. i measured a gallon of water at a time, by weight, for the best accuracy. pour into the pot. mark the level with a sharpie. the sharpie marks stay intact for a surprisingly long time. every other use or two, i just remark before it wears off.
i intend to carefully measure the distance from the top, transfer measurement to the outside, then use a punch and hammer (with a block of wood on the inside) to put a permanent dimple there.