Note 4 — Chapter IX · THE NORTH STEAMING ERROR
Reading edition
The value of the north steaming error is numerically equal to (a K cos C)/cos L, where K is the ship’s speed, L the angle of latitude, C the angle between the course and the north and south direction, and a a constant involving the speed of rotation of the earth. In the Sperry correction mechanism the value of the quantity a is represented by the radius at which the pin L lies from the centre of the latitude dial.