Have you ever wondered what artists were doing when they peered over an outstretched pencil at a subject? This strange-looking practice is a very useful method of measuring the sizes and angles of the subject by using your pencil as a ruler, and establishes a more accurate drawing. These aren't absolute measurements—rather you are looking at the relative proportions. For example, if you view your model's head from where you are sitting and use your pencil to measure the proportions, it might appear to be around an inch tall, but your actual drawing might be four inches tall. So, in this example, one inch is your “base unit” of measure, and everything that you measure as one inch with your pencil will be four inches in your drawing.
To measure sizes using your pencil, grip the pencil in your fist and place your thumb near the top of the pencil. Stretch out your arm from the shoulder, elbow straight, and line up the pencil with your chosen “base unit” of measurement (in the previous example, the model's head). Line up the top end of your pencil with the top of the chosen object and slide your thumb down the pencil until it lines up with the bottom of the object. The distance between your thumb and the end of the pencil establishes the base unit of measurement. When taking other measurements, be sure to stretch out your arm to the same degree and stand in the same place. Frequently return to check your base measurement, as slight changes in position can substantially alter the apparent size.
In figure drawing, the base unit is usually the distance between the top of the head and the chin. Line up the top of the pencil with the top of the head. Slide your thumb down the pencil until the tip of the thumbnail lines up with the bottom of the chin. This is one head-unit. Keeping the arm extended, you can then drop the pencil so the top lines up with the chin. Where your thumb lines up on the subject is now one head-unit down from the chin. Once the head is sketched in, for reference, make a small mark one head-unit below the chin you've drawn. This should be the middle of the breastbone. Continue in this manner down the figure, marking in each measured point.
You can use the same method to judge other distances—widths, spaces between objects, and diagonal measurements. This is especially useful when you have already sketched some elements, which you can then use as base measurements. Once you've taken the base measurement from an object, be careful not to move your thumb. If the thing you are measuring is smaller or larger, guess how much the difference is and make your mark correspondingly smaller or larger on your drawing. If the difference is too big to guess, choose a different reference point. In portrait drawing, smaller details, such as the eyes, can be used as references. You can use any clear, suitably sized element in drawing, whether landscape or still life, as a reference point.
Checking angles and distances keeps proportions correct.
A simple way of measuring angles is to use two pencils, holding them in an outstretched hand. First, line up one of the pencils with any established vertical or horizontal in or near your subject (a door frame, a chair, or other prop), then rotate the other pencil to line up with the limb or other element of the subject that you need to locate.
Once the angle is established, carefully move the pencils to your paper, line up your horizontal or vertical, and transfer the angle to the drawing. This needn't be an actual line—finding several angles from known points to a questionable point can help you locate it accurately: sketch in each line, and they should intersect at the point's location.