Trigonometry tool with rotary disc, has radial indicator for placing in given angular position and window with grid pattern covering space in center of disc

摘要

The disc (12) has an indicator (12a) extending in the radial direction from the disc rotation axis over a length equal to the radius of a concentric space (11a) inside this disc. Rotating the disc allows the indicator to be placed in a selected angular position and a rough calculation of an angle value such as its sine or cosine can be made using a transparent window (13) with a grid pattern covering the concentric space in the middle of the disc. An exact mathematical expression can be applied to the disc and if necessary it can be displayed by lifting a flap (15) in the panel (11) holding the disc.