GB647270A - Improvements in or relating to apparatus for indicating a co-ordinate position on a chart - Google Patents

Abstract

647,270. Maps &c. DECCA RECORD CO., Ltd., and COPPING, J. B. Nov. 21, 1947, No. 30970. [Class 146 (ii)] Apparatus for indicating on a chart a geographical position represented by the intersection of two position lines of two families of position lines comprises the combination of a geographical area chart 36, so distorted that two intersecting families of hyperbolic lines on the true map are represented by two intersecting families of parallel straight lines forming a co-ordinate system, a first member 17 movable relative to the chart in one of the co-ordinate directions, a second member 33 carried by the first member and movable relative thereto in the second co-ordinate direction and means for setting the members in accordance with their respective ordinates so that the required position is indicated by a selected point 39 on the second member 33. The member 17 comprises a slide bar 17 made up of two parallel strips 29, 30 of transparent material secured at each end to a member 15 slidably mounted between fixed parallel bars 11, 12 along the top and bottom of a casing 10, the member 15 being traversed along the bars 11, 12 by means of a lead screw 18 engaging a lug on the member 15, the screw 18 being operated by knobs 24 on a shaft 23 in bearings in the sides 13, 14 of the casing 10. The second member 33 is preferably of transparent material having a central hole 39 and the member 33 is slidably mounted between flanges 31, 32 on the strips 29, 30 and is movable along the slide bar 17 by means of a wire 34 running over freely mounted drums 35 and wound round a drum 28 mounted on a shaft 25 and between lugs on the member 15 through which the shaft 25 passes, rotation of a knob 26 rotating the drum 28 to move the indicating member 33 but rotation of the knob 24 merely causing the drum 28 to slide along the shaft 25. The chart 36 is mounted on an aluminium sheet inserted between the member 15 and slide bar 17, the sheet having slots 37 to engage threaded locating pins 38 on the casing 10, nuts being tightened on the pins 38 to secure the chart 36. A pointer 40 on the slide bar 17 may be provided opposite a scale 41 and opposite a scale 42, a pointer 43 may be provided to be operated through a fixed drum 44 secured to the shaft 25 so as to move with the member 33. Stops may be provided to limit the movement of the member 33. The scale of the distorted chart may be made non-linear to reduce distortion. A pocket for spare charts may be provided on the underside of the casing and a sliding lid may be provided for the upper face. The charts may be covered with a transparent film and different charts mounted on both sides of an aluminium sheet. Lighting may be provided. The charts may be marked with any required information of route, radio responses, bearings, mileage and so on.