Ship's dimensions should be entered using the overall length
and width of the ship indicated by the values A, B, C, and D in the
following figure.
Ship's dimensions (A+B and C+D) should be identical when entering
internal and external reference points.
Figure A
In the rare case of an EPFD antenna installed in the portside
corner of a rectangular bow, the values A and C would be zero. Should
this be the case, one of these values should be set to 1 in order
to avoid misinterpretation as "not available" because A=C=0 is used
for that purpose.