3 different sized cubes for calibration. As files indicate. Yes, there are lots of calibration cubes with the same information showing below. It's not hard to design and make cubes and I made them and placed them here primarily for my own convenience.
e= expected dimension
o = observed dimension
s = current number of steps per mm
(e/o) x s = your new number of steps per mm
e will always be the value of the size of cube you are calibrating against.
o will always be the actual size of the cube you printed.
s will be your current setting for the steps/mm.
If you print all 3 cubes, the value for your new number of steps/mm should theoretically be the same (or pretty darn close) for all 3.
It usually shouldn't be necessary to do all 3.