Geometry Compasses

A self-centring compass holds its radius when the point is pressed and is worth the difference for anyone drawing accurate constructions — a standard hinge drifts, and a circle that closes 2mm out is a wrong answer. Check what the compass takes: some use a standard pencil, others a lead that needs replacing. For classroom sets, a locking wheel survives a term better than a friction joint. Often bought with protractors or as a geometry kit.