You see form more truly also, when the perception of it is founded on a mass or a line indicating the larger character of it. It saves time for you, too. You do not have to rub out so much. The great lines and planes once established, everything else falls naturally into place. Spend much time over this part of a drawing. Cut the time you give to a drawing into parts, and let the part given to the laying in of larger proportions be from a third to a half of the whole time, and study and correct these until they are right.
Once these are right a very slight accent tells for twice what it would otherwise, and so you need much less detail to give the effect.
=Modelling.=--In the same way that you have laid out the proportions in mass, lay out your proportions of light and shade. Model your drawing by avoiding the small until the large variations of shade are in place. Avoid seeing curves in relief as you have avoided curves of outline. Try to analyze the modelling into flat planes, each one large enough to give a definite mass of relief. Don't be afraid of an edge in doing this. Let your flat tone come frankly up to the next tone and stop. This again is not for any effect in itself, but only for facility and exactness. Later you can loose it as much as you see fit in breaking up the drawing into the more delicate planes, and these again into the most subtle.
Study first the outline and then the planes. Constantly compare them as to relation; you will find it suggestive. Remember that your aim is to produce a whole, not a lot of parts, and although a whole includes the parts, the parts are incidental.
=Measurements.=--You will always have to use measurements for the sake of accuracy. Probably you will never be able to dispense with them. The best way would be to take them as a matter of course, and get so that you make them almost mechanically, without thinking of it. You will save yourself an immense deal of time and trouble by accepting this at once; for accuracy is impossible without measurements, and the habit of accuracy is the greatest time-saver.
Hold your charcoal in your hand freely, so that your thumb can slip along it and mark off parts of the object when you sight at them across the coal. Measure horizontal and vertical proportions into themselves and into each other. Height and breadth are checks to each other. If the height is a certain proportion of the breadth, then the smaller proportions of height must have equivalent proportions to each other _as well as to breadth_. Measure these and you are sure of being right.