Already many years ago Captain A. Vreugdenhil proposed the use of visual aids to supplement the sound signals used to indicate changes in heading. His idea of using visual aids was based on the erratic behaviour of sound and the consequent possibility of misinterpretation of sound signals.

Choosing between two possible systems, the directional illuminated arrow and, for example, flashing lights, he preferred and constructed an illuminated arrow, visible as such from a distance of approximately 1½—2 miles. He was against the use of synchronous flashing lights, pointing out the large difference in speed of propagation between sound and light signals and consequent possibility of errors when different sound signals are given in quick succession.