NavList:

Thanks all for your replies, lots of very useful points,

I have just had a look at some sample pages from HO249/AP3270 and it does indicate the difference between zero LHA and 1 degree LHA. Should have thought of doing this myself.

In one table there is zero difference, in another 1'. It does illustrate what is often described as the Sun hanging for a while.

I do understand the time is not important, it is the moment of LAN that is important but once LAN has been established as accurately as possible we do need the time of the sight to extract declination from the Almanac.

Thanks again

Mike