The Helix Precision Compass is a great value compass ideal for students and school pupils. The compass\' thumbwheel provides enhanced accuracy and precision and its double knee joints help you draw perfect smaller circles. This metal compass also has a geared head for centring. This is an easy-to-use compass for drawing perfect circles, and is perfect for students and school children studying maths or design subjects.Also contains 2mm replacement leads and additional screws and nuts.