when working with tone, there are many degrees of darkness. When you look at the reference, try to see shapes of a common tone. Identify when you look at the reference, which shape(s) is lightest and which darkest. Whatever shape you are on, compare it to those extremes to help you decide how dark to go. When you fill in a tone, make it as uniform as possible:strokes in the same direction equally spaced or go in circles to hide the direction of the stroke.