I have prepared a new version of /gmath/, the gnomonics add-on for
Microsoft Excel that was announced in NASS' Compendium 24:4 (December 2017).
Documentation for the new version is available as a PDF file at
http://va7lel.ca/sundial/gmath.pdf
The updated Excel Add-In is available for download from
http://va7lel.ca/sundial/gmath.xlam
Existing installations can be updated by overwriting the gmath.xlam file
in your Microsoft Add-Ins folder (see documentation). You must do it
while Excel is _not_ running.
_Bug fix_
Values returned by the functions /geot/ and /gdcl/ were systematically
wrong. When compiling the associated tables, I forgot to specify noon as
the required time of day, meaning the functions always returned values
applicable to the previous midnight. In the case of Equation of Time
values returned by /geot/, this resulted in an error of less than about
0.1 seconds. In the case of solar declination returned by /gdcl/, the
discrepancy was insignificant at the solstices but as much as 0.2
degrees near the equinoxes. The functions /geoted/ and /gdcled/ were not
affected by the bug.
_Other changes_
Functions based on formulae involving the obliquity of the elliptic now
include an adjustment for nutation. For ordinary sundialing purposes the
change is insignificant: the new obliquity values differ from the
originals by only about 9 arcseconds.
The new version retains an existing circumvention for a deficiency in
Excel 2011 for Mac which led to failure of some gmath functions.
Cheers,
Steve Lelievre
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