Comparative Measuring for Reliable Drawings
How to compare one part of a drawing with another, using halfway marks and plumb lines instead of guesswork.
Comparative measuring asks a simple question. Is this part as wide as that one, or half as wide, or a little more? You ask it of the subject, then you ask it of the drawing. Where the answers disagree, the drawing changes. The method sits beside sighting with a pencil. The pencil gives you a unit from the world. Comparison tells you whether the page obeyed it.
Find the halfway mark
Choose the largest shape and find its middle. On a bottle, the halfway height may land on the shoulder, not where a label wants it to. On a face, a point halfway from crown to chin often sits near the eyes, lower than memory suggests. Mark that halfway line on the drawing early. If the feature that should sit there is nowhere near it, you have found the error while it is still cheap.
Measuring Proportions with a Pencil is how you check the halfway point against the subject without leaning in. Take the whole height as one unit, half it, and see what arrives at the thumb. Then look at your page and see what arrived there instead.
Plumb lines and alignments
A plumb line is an imaginary vertical. Hold the pencil vertically at arm's length and notice what falls beneath a point. The handle of a cup may hang to the left of the rim's edge. An ear may sit under the brow, not behind it in a vague somewhere. Draw a light vertical on the page and place those parts on it.
Horizontal alignments are the same idea turned over. The far edge of a book may line up with the rim of a glass. If the drawing misses that alignment, the objects will not share a table, however carefully each was outlined. Using Negative Space to Make Stronger Drawings and Designs catches the shapes between them. Comparison catches the shared edges.
Check the drawing against itself
Once a few marks exist, measure the drawing with the same cruelty. If the subject says the gap between two cups is one cup wide, the gap on the page should be one cup of the page's cups, not one cup of a different scale. Inconsistent scale is the usual quiet failure. Each object is plausible. Together they could not exist.
Drawing Hands from Life in Short Sittings benefits from one comparison in particular: the length of the middle finger against the length of the palm. If the page disagrees with the hand, shorten the finger before you draw the nail.
Three questions, then a correction
Do not measure fifty points. Ask three questions. What is halfway? What sits on the same vertical? What width equals another width? Correct the worst disagreement first. A small error in an eyelash is less urgent than a head that is too long.
Write the comparison you failed in the margin, in words. Next time you will look for it sooner. A drawing session that ends with a correction is a session that measured. A session that ends with shading over a known error is a session that hid.
Frequently asked questions
Is this the same as using a ruler on the object? No. A ruler on the object gives millimetres you then have to scale. Comparison gives a ratio you can use at any size of drawing. Keep the ruler for the page if you want a clean border, not for the pear.
How often should I check? Once when the large shapes are blocked, and once before you commit to darks. Checking every minute produces a stiff drawing. Never checking produces a confident wrong one.
What if the subject moves? Take the big comparisons first, halfway and the main alignment. Let small edges go. A moved cup cannot be measured back into existence. Note that it moved, and keep the proportions you caught.