Furuno BB FAR28x7 - Manual (Page 293)

APPENDIX
AP-45
4. 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).
62 °N °N
60 °N
135 °E 139 °E
Real cursor position
Cursor position
indicated
LAT E
Real cursor position
Cursor position
indicated
96 nm
θ
OS position
R: Error
Distance error in direction of longitude due to latitude