Meridional difference (m) or D.M.P
M.P.= 7915.704486 Log.( 45 + Lat./2) – 23.268932 Sin Lat.- 0.0525 sin.³ lat.
or
M.P.= 7915.704 Log.( 45 + Lat./2) – 23.3 Sin Lat.
D.M.P. or m. = M1 – /+ M2
M1 = M.P.1
M2 = M.P.2
PROCEDURE OF MERCATOR SAILING
1. Find the d.lat and the d.long and also the difference of meridinal parts for the two latitudes.The rule for D.M.P.will always be the same as that for finding d.lat.,I.e.same names take the difference ; difference names take the sum of the mer.parts.
2.Find the course using the formula ; d.long/d.m.p = tancourse
3.Find the distance using the formula distance; distance = d.lat. x sec.course
Determining course from course-in-quadrant
For C (course-in-quadrant):
Prefix N or S depends on L1.
Suffix E or W depends on direction of DLo.
For each quadrant of C:
NE: Cn = C
SE: Cn = 180 - C
SW: Cn = 180 + C
NW: Cn = 360 - C
