The use of a measuring device to check the relative size and position of a subject and its individual parts is known as sighting. A measuring device is any straight and narrow tool with clean edges, we will most likely always use a pencil as our measuring device in this class, and I will refer to the measuring device as a pencil below. The goal is to create a unit of measure for comparison throughout your drawing, so how do we do that?
Be consistent. Hold the measuring device in the hand you are not using to draw, and extend your arm fully. Make sure the pencil is at a right angle to your line of vision (imagine being pressed into a microscope slide so that you become a flat plane) keeping your pencil parallel to you, not pointing forward or backward.
To gauge proportions, line up one end of your pencil with one edge of the object and adjust the tip of your thumb on the pencil to line up with the opposite edge of the subject. Between your thumb and the top of your pencil is one full dimension of the subject. Without moving your thumb position, rotate your hand to compare your first measurement with another major dimension of the
subject or space between objects.
To assess the position or angle of a subject, line up your pencil along the angled edge and bring that down to the page in the appropriate location. Use this process to understand the degree of the receding edge or the slope of a curved edge. This is also useful in drawing relations between subjects.