Product information:

Simple and Practical Draughting System. You may now draw straight , parallel lines without a ruler or drawing board. Simply place normal photocopy or writing paper over the plastic sheet of the Technical Drawing System, and using any hard tipped pen or pencil, draw a line horizontally or vertically anywhere on the paper. The lines you draw will be perfectly straight. Now you need a line at an angle, simply move the paper to the angle of your choice (marked on the plastic sheet and draw your angled line. As simple as that.