it can also be done by using a piece of tubing attached to the drain and held up against the carb body... fuel in carb and let drain. will flow inside clear tubing to the exact level that it is at inside the bowl.
problem w/ this method is the requirement to disassemble, assemble, fill, set up tube, drain, measure, repeat entire process as needed!
all w/ only 2 hands! and 4 carbs!