The Effect of Two-Axis Vibration on the Legibility of Reading Material

The legibility of reading material subjected to single-axis sinusoidal vibration is believed to be dependent on the form of the nodal images. It has been hypothesised that when motions in two axes combine to cause reading material to move with a circular motion the absence of nodal images will greatly reduce legibility. Nine subjects wore required to read arrays of one hundred digits of the form recommended in British Standard 3693A. The effect on reading errors and reading time of seven frequencies of vibration (from 3 to 10 Hz) and the three double amplitudes (4·7 to 8·7 mm) were investigated for vertical, horizontal and circular motion of the digits. It was found that errors and reading time were appreciably greater for the circular motion and increased with increasing vibration frequency and displacement. The legibility of some digits was less affected by the vibration than others and it was found that many reading errors were due to confusion between digits that appear similar when vibrating. It seems probable that a system of digits could be devised to reduce the effects of vibration on reading errors and reading time and it is concluded that the dual axis nature of many vibration environments may be of great practical importance.