From: Michael Bradley
Date: 2018 Mar 11, 10:49 -0700
No problem at all to plot an astro LOP onto an ECDIS screen, based on an astro chartwork method used (at least) by the UK merchant marine for decades:
Use the Longitude by Chronometer reduction method formula with any convenient Assumed Latitude.
Then compute / look up the Azimuth.
Use the ECDIS to draw a detached electronic bearing line (EBL) at 90 degress to the Azimuth from the start point given by the Assumed Latitude and reduced Longitude.
It is not necessary to use a whole number Assumed Latitude for the Longitude by Chronometer reduction formula.