In a microwave landing system the individual words of a train of command words generated by the antenna beam steering unit are applied to a polynomial generator where each is, seriatim, summed with a polynomial check word generated in a previous operation. The result is shifted once
An optical position code detector which senses information that is recorded on a record carrier. The record carrier preferably has scan marks for synchronizing operation of the detector and at least one track with positionally encoded data marks which include one or more imprinted al
