When, in 1958, B.O.A.C. undertook to evaluate the Marconi AD 2300 doppler navigator, the exercise was planned with great care. The aim was to determine the performance of the system in quantitative terms, and to express the results so that their operational significance was clear.

In preparing this evaluation, three objectives were stated, as follows:

(a) To obtain quantitative data on the performance of the AD 2300, considered as a measuring device, in terms of accuracy, consistency and reliability.

(b) To obtain qualitative information on the optimum methods of system application, by reference to observer reaction.

(c) To introduce the doppler system in operation to a wider selection of B.O.A.C. flying staff, in order to develop a body of informed opinion.

It is the first of these objectives with which this paper will deal.