In the Mercator projection used to transpose the surface of the Earth to a flat chart, the curved Meridians of Longitude have been straightened and in doing so, a distortion has occurred affecting the Latitude scale. By straightening the meridians, and making them all parallel, the length of one minute of difference in longitude (D.Long) is now the same throughout all Latitudes. Although this overcomes the distortion in the Longitude scale negating the need for Departure. The Meridional Parts Tables give the number of Meridional Parts for every degree and minute of Latitude measured from the Equator. As Meridional Parts are of the same units as the Longitude Difference, the plane triangle that represents the course and distance between two points on a Mercator chart, can then be solved by applying simple trigonometry theory. There are several characteristics of the Mercator chart that students should be aware of in order to use it correctly.