Clear plastic construction. The 360° protractor head has scales calibrated to be used with the ISOM (International Standards of Measurement) system. This high resolution model has a white background behind the numbers and lines that assures a high contrast for added readability. Reads 0 ̊ to 90 ̊ and 0 ̊ to 180 ̊ in 1 ̊ increments. One arm has a linear scale in inches and centimeters. 6.25 inches(16cm) long.