Technical Illustrator on the project using a set of plastic venier calipers.
Edges Take a look at the vernier calipers.
That is a grip for your thumb. Slide it back towards the tail end of the calipers and the jaws open as shown on the dial calipers. If you are measuring the outer edge of an object, like, let's say the head of an ushabti figure, you would open the jaws of the calipers and slide them carefully over the head of the ushabti. Read the sliding scales along either top or bottom or read the dial to see the size of the head. Care must be taken to assure that your calipers are straight.