45cm Classroom Compass Ruler for Chalk. This 45cm Classroom Compass Ruler is a durable and practical teaching tool designed for drawing large, accurate circles on chalkboards. Made from environmentally friendly ABS, it is sturdy, nontoxic, odorless, and resistant to deformation, ensuring longterm use in busy classroom environments. The smooth, burrfree surface protects hands while offering excellent wear resistance and the ability to withstand multiple drops. An adjustable screw mechanism allows teachers and students to draw circles of various diameters with ease. The dualpurpose clamp securely holds both chalk and marker pens with a diameter under 2.5cm, making it versatile for different teaching setups. A strong suction base keeps the compass firmly positioned without slipping, ensuring clean, precise results every time.