The route direction-finder is a device giving an accurate directional reference. It uses two distant transmitters, A and B, radiating two continuous waves, the frequencies of which are different but very proximate. The paper was presented at the Paris convention on automatic navigation.

Classical methods of navigation by dead reckoning have been considerably improved in recent years by the use of autonomous systems such as doppler and inertia which enable true speed to be measured. When using these systems, the principal cause of errors is the unreliability of the directional reference, which may be the meridian or any arc of a great circle, since it is with respect to this that the speed vector is obtained. The directional reference is given by the magnetic compass which often has an error of up to several degrees or is given by gyroscopic devices which can have considerable drift after several hours' operation. Errors in directional reference are especially marked in polar regions where magnetic or gyro compasses cannot be used.