AbstractIn co-operation with Messrs. Fairey Surveys Ltd. and the School of Military Survey, an experiment has been run with a view to determining the feasibility of point signalisation for 1/40,000 scale photography, and the accuracy of co-ordination of such signalised points when the photographs are suitably exposed on fine grain film in an RC8 camera and measured in first-order plotting machines. The paper describes the experiment and the results obtained.