Rotring Compass, Single, with Extension Bar and Inking Attachment, 2 mm

Rotring Compass, Single, with Extension Bar and Inking Attachment, 2 mm.

A drafting compass draws a circle of a set radius and holds it — the joint stays where you put it while the point pivots and the lead arm sweeps round.

What separates a good compass from a cheap one is whether that setting survives the sweep. A joint that drifts by half a millimetre gives you a spiral instead of a circle, and on a technical drawing that is the difference between a drawing that closes and one that does not.

• Holds its radius through the full sweep
• Takes 2 mm leads — sharpen the lead to a chisel for a crisp line
• Set the radius against a ruler, not by eye