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Hello Tony,

Quick calculation on 31-12-2019 (who is doing celestial on that day??) at 12:00 GMT.
With diff -8 GHA=359°17' (original value)
With diff -10 GHA=359°16' (corrected value)
The USNO website gives for these input GHA 359°17.3'

Looks that diff -8 is better. I have no idea how I calculated this particular day 3 years ago.
All the other days diff values are clear.  E value this day minus E value next day
Ascending + sign, decreasing - sign.

The same calculation for 1-12-2019 12:00GM
With diff -6  GHA= 2° 46' (original value)
With diff -5  GHA= 2° 47' (correct value)
The USNO website gives for these input GHA 2°46.5'
So just between or as rounded to whole value 2° 47'
I keep now your corrected diff -5 value, because it is in line with the other calculations.

Well it are all minor differences, but we must try to get correct as possible.

For most of my calculations I use TI-89 Starpilot calculator.
If I do it longhand I use the SunsTable4 to get GHA and Dec.
The last Nautical Almanac that I have bought was the 1995 edition.
It is on the bookshelf as curiosity.

Kind Regards
HermanD  52°N 04°E