PRECISION 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 accurate 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 spring bow head and thumbwheel could prevent from unintended slide.colour: blackMaterials: MetalPackage Contents:1 * Precision Compass2 * Spare Screws3 * Spare LeadOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.