Made by Heath Navigational Ltd. Station Pointer, also known as a 'Three arm protractor'. The station pointer is used to determine location of a ship.
The navigator first determines the directions to three visible objects ashore and then separates the legs by the angles between the adjacent objects. He positions the station pointer on the chart and lines up the three arms with the objects ashore. There is only one solution to the procedure and that is that the ship?s location on the chart is the intersection of the three arms (the centre of the protractor). The ship?s position is marked by a pin prick on the chart or a pencil may be used through a centre hole. This process is especially useful in coastal surveys when charting soundings. This same procedure can be used on land to determine the location of the point where the observer is located.
The Station Pointer has a 8 inch diameter steel protractor graduated in degrees and three 15 inch metal legs radiating from the centre of the protractor. The middle leg is fixed to the protractor; the other two are free to rotate to any angle (greater than 5° from zero) relative to the fixed middle leg. There is a release lever to allow quick re-positioning of the legs. The unit comes with three connector arms which extend the leg lengths to 27 inches if desired. The entire unit is stored in a handsome (but scratched) wooden case. Total weight is: 5.3kg Comes with original key and loupe.