Accuracy of reproducing angles: Is a right angle special?

The ability to set the angle of a 'V' to a designated value in the following three conditions was compared: (1) verbal designation of V angle; (2) initial 30 s visual demonstration of the designated V angle; (3) verbal designation of V angle plus feedback after every setting. The designated angles were 90° and 45° plus three arbitrary angles (65°, 125°, and 145°). Each run comprised thirty consecutive settings. To ensure that our observers based their settings entirely on V angle it was arranged that line orientation did not provide a reliable cue to V angle. In condition (1), accuracy of setting V angle was significantly worse when the designated angle was other than 90° or 45°. This was not the case in condition (2), indicating that observers maintained a memory of the initial demonstration throughout a run of thirty settings. Setting error was not significant in condition (3) for any of the five angles. However, even in condition (3), setting-to-setting variability was significantly lower for the 90° angle than for the other angles.