MATH COMPASS - Made for mathematical geometry and art drawing. Unique design to prevent slip while drawing. PRECISE ADJUSTMENT - The adjustment knob enables students to produce geometric constructions. You can lock the compass in place and have it actually stay when writing. ADJUSTABLE SIZE - Maximum diameter up to 10 inches, minimum for 1/8 inch. You can draw all kinds of circles. ALL-METAL MATERIAL - Made from high quality parts and solid construction, durable enough to last for a long time. Three additional leads are easy to replace when needed. Stability: The compass with bow head and thumbwheel could prevent from unintended . colour: black Materials: Metal Package Contents: 1 * Compass 2 * Spare Screws 3 * Spare Lead Only the above package content, other products are not included. Note: Light and different displays may the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.