Radio navigation plotter

Claim 1

In a radio navigation plotter for an aircraft or watercraft comprising: a back plate and a front plate concentric with each other, said front plate having a 360* calibrated scale extending circularly about its center, and said back plate having a diametrical North-South line thereon, said back plate being rotatable with respect to said front plate about their common center to displace said NOrth-South line angularly from alignment with the o-180 axis of said 360* scale on the front plate according to magnetic variation at a particular geographic location; and an elongated arm pivoted on said plates to turn about their common center, said arm extending laterally beyond one side of the plates and presenting a straight edge which extends radially outward beyond said plates, said arm having a marker aligned with said straight edge and located at the opposite side of the common center of the plates to designate on said scale on the front plate an angle 180* from the angular position of said straight edge; the improvement which comprises; a disc having a circular compass scale thereon concentric with said scale on the front plate and registering with the latter said disc being rotatable relative to said front plate about said common axis to displace said scale on the disc along said scale on the front plate in accordance with the magnetic heading of the craft; said marker on the arm being registrable with said scale on the disc in accordance with the relative bearing so as to designate on said scale on the front plate the magnetic bearing of the craft to the radio station.