Henry's "penograph" is also known as a pantograph. A pantograph is used to draw copies of a picture. It works in the following way: a blank sheet of paper is placed next to the picture to be copied. The outline of the picture is traced using a pointed tool attached to one end of the pantograph. At the other end of the pantograph is a pencil. As the tool is moved, the pencil moves in the same direction, copying the lines onto the new sheet of paper. The pantograph can be adjusted to draw the picture bigger or smaller than the original.

Today, artists, architects, and engineers use copying machines, overhead projectors, or computers to make copies of pictures.