Formation of the Observer Corps
Eventually the system was extended to cover the whole of England and Wales.
The Observation Posts were usually simple constructions generally consisting of emplacements surrounded by sand-bags.
In addition the Observation Posts were issued with an instrument (see photo) which allowed readings to be taken in both direction of movement and aircraft height.
A standardised reporting format based on a common map reporting grid system was established; this allowed readings from two or more posts to be used to provide a more accurate mapping of aircraft position, direction and height.
Training in aircraft types was improved by the issue of aircraft recognition cards