The heart of the B.O.A.C. Navigation Procedures Trainer (NPT) is a general purpose digital computer (Elliotts 905) and the programs have been contained within a memory store of only 16,000 words. There are fourteen cubicles for the pupil navigators and one for the instructor. At each cubicle is the usual chart table and stowage for manuals; navigation information appears on a CRT screen in the form of letters and numbers. Requests for radio bearings, astro sights and so on are conveyed to the computer by means of a typewriter keyboard and some simple codes which are shown on a plaque to the left of the CRT. Only a few of the keys are special ones.