An Improved Instrument for Determining the Compass Course of a Ship from the True Course as Indicated on the Chart or for Determining the True Course from the Compass Course.

摘要

6777. Jones, C. P. March 24. Bearings a n d courses, determining; compasses, magnetic.-Figs. 2 an d show in section and plan, respectively, an instrument for mechanically allowing for the compass variation in the determination of ships'bearings. A circular disc 1, with a bevelled and graduated limb, is made with a circ ular groove on its face, in which four graduated segments A, B, C, D are adapted to slide. The centre of the disc is left transparent and is fitted with cross-wires 4. To facilitate the readings, a lens 10 may be used. To determine the desired compass course, the instrument is first placed down on the chart over the true course line G-G with its N-S line true. One of the divided segments is then adjusted with its zero on the line G-G, and then, opposite the number corresponding to the variation, the compass bearing to be steered can be read off. The instrument may be used in a similar way to convert compass readings. In a modification, a straight edge is pivoted to the centre of the disc.