Combined slide rule and protractor - has graduated transparent rule pivoted at centre of semicircular disc

摘要

The combined protractor and slide rule for trigonometric functions comprises an opaque or transparent semicircular disc (2), to which a transparent graduated rule (6) is pivoted at its centre, the length of the rule (6) being at least equal to the radius to the disc (2). A rectangular plate (3) is attached to the bottom of the disc (2) with a slot (4) parallel to the diameter of the disc (2) along which a further graduated rule (5) slides. The pivoted graduated rule (6) has a cursor (8) moving along its, along the length of a coloured line (7) marked on the rule, with the cursor (8) carrying a rectilinear line. The length of the slot (4) in the rectangular plate (3) is such that for each position of the sliding graduated rule (5) one of the scale lines marked on the latter coincides with the centre of the circle of the disc (2).