NavList:

Dear Antoine,

Many thanks for the description of the theodolite setup.  The results are very impressive.  The effort you have gone to in achieving that accuracy makes me further appreciate the unsung and unrecognized people who first mapped the earth's land and oceans with sextants and theodolites.  We truly do stand on the shoulders of giants!

I had a look at the pages with the formulae for altitude corrections in the almanac, as David Iwancio suggested.  I'm in the process of creating a spreadsheet to automate the procedure, but in the meantiime I decided to see if online tools were already available for the task.  I found Henning Umland's site https://www.celnav.de/sightred.htm and recalculated my four 'sightings' with the web app on that page.  

At the end of this post is a repeat of my numbers with the web app calculations of Ho inserted.  Points of interest:

1. The difference beween Ho from the almanac tables  and that from the web app was just 0.1' at low elevations, falling to 0, at medium elevations.  On this occasion, the almanac's altitude correction tables performed acceptably well if the web app is correct.

2. The difference between Ho from the Henning Umland web app vs the USNO web app clone was 0.4' at low elevations, rising to 0.6' at medium elevation.

I think this supports your comment that the software may need improvement.  To be fair, though, I believe I was using it for a purpose for which it may not have been designed.   In its primary role of detecting GPS spoofing, I suspect the small errors discussed here may be of no significance.  

The reltively small errors arising from use of the almanac's lunar altitude correction tables in this case seem a fair trade for the simplicity of their use if calculators are unavailable. 

This has been a great learning exercise for me and I am very grateful to you, David Iwancio and Bill Ritchie for taking the time to help me to widen my understanding of our inconstant moon and its use in celestial navigation.

Regards,

Lance

UTC date: 02AUG22, GPS position: 42° 49.4'S 147° 15.7'E.

GPS Anti Spoof Pro (ASP) settings: Body: Moon, LL, sea horizon, no delay, T=11-14°C, P=1007 hPa/mb. Index correction -1.0'.  Height of eye 2.9m.

Time                     Hs                    Almanac Ho  Web app Ho   USNO Hc

01:02:06 UTC ASP Hs=12° 53.1',   Ho 13°54.5', Ho 13°54.6',  Hc 13°54.2'  difference 0.4'

01:55:07 UTC ASP Hs=21°39.3',    Ho 22°39.9', Ho 22°40.0',  Hc 22°39.5'   difference 0.5'

04:12:17 UTC ASP Hs=39°18.3',    Ho 40°11.6', Ho 40°11.6',  Hc 40°11.0'   difference 0.6'

05:55:58 UTC ASP Hs=43°07.4',    Ho 43°58.5', Ho 43°58.5',  Hc 43°57.9'   difference 0.6,