Study to improve middle latitude sailing

In this paper the thoroughgoing analysis is made about the three calculating methods of middle latitude sailing, these are middle latitude sailing ,mean latitude sailing and middle geocentric latitude sailing. A new sailing, namely proper latitude sailing, is presented, which by means of spherical trigonometry solves the questions about rhumb line sailing on the surface of the oblate spheroid. Some wrong conception of the above mentioned calculating methods are clarified. The proper latitude sailing and the conclusions drawn are both theoretically and practically valuable.