The device consists of a series of carefully constructed angles which are photographed and then printed on contrast process Ortho film to give narrow black lines on transparent celluloid. It is used by moving it laterally over the shadowgraph of the curved coleoptile being measured until the bottom and top of the coleoptile are oriented parallel with the bottom and top lines of one of the angles. Measurement of coleoptile curvatures with this device is rapid and accurate.