I think the purpose behind the double image is as the range changes so does angle A. They figured an easy and quick way to figure out angle A and put it into the equation would be to superimpose an image and have you line up the mast to the water line. If x=mast height and angle A=the angle between ownship and target mast height and y equals range than. Range= x multiplited by the cotangent of angle A. it's just an easy way to figure out that equation without a pencil and paper, remember they had no calculators
|