Longitude Error Table (On 96 Nm Range Scale) - Furuno RP-250 Operator's Manual

6. OTHER PLOTTER FUNCTIONS
6.2

Longitude Error Table (on 96 nm range scale)

The longitude lines concentrate on the north pole and south pole, namely, 1 nm
is equivalent to 1 minute at 0 degree latitude, 2 minutes at 60 degrees latitude, 3
minutes at 70 degrees latitude and so on. For this reason, a longitude error
occurs on the radar display. For example, when own ship is at 60 N and 135 E,
even if the cursor indication is 62 N and 139 E, the real cursor position is
deviated to the left (west) side. The table below shows the longitude error,
represented from 0 to 90 at 96 nm from the radar center (own ship).
Real cursor position
62 N
60 N
135 E
Distance error in direction of longitude due to latitude
28
Cursor position
indicated
139 E
Real cursor position
N
96 nm
LAT
OS position
R: Error
Cursor position
indicated
E