Fangrui Product Details 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 When Needed. Stability: The Compass With Spring Bow Head And Thumbwheel Could Prevent From Unintended Slide. Colour: Blue/black Materials: Metal Package Contents: 1 * Precision Compass 2 * Spare Screws 3 * Spare Lead Only The Above Package Content, Other Products Are Not Included. Note: Light Shooting 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.