By W. D. Farris
The instrument represented by the accompanying drawing is designed to determine the actual distance a ship must pass off a light or point. The elements in the determination of said distance are two bearings and the distance run between them.
The angle made by each bearing with the course and the distance run between them are determined first. The operator then sets the first angle on blade 5, and the second angle on blade 8.
The next step is to set the small arc on the square the same as blade 8. Now, slide 15, carrying blades 12 and 13, is moved out along blade 8 until the distance run on scale 12 coincides with the inner edge 6 of blade 5. The distance the ship will pass off the light or point in question will be registered on blade 13 in coincidence with edge 11 of blade 10.