I am trying to understand the reason(s) for the slight differences
in occultation times as calculated by Guide8b and Occult3 (latest
version). For example, my latitude is N43 2' 7.8" and my longitude
is W88 25' 5.2" with an elevation of 280m. I am looking at the
December 7, 2004 occultation of Jupiter by the Moon. Occult3 lists
the time of first contact for my location as being 8:49:56 UTC while
Guide8b shows the time of this event to be 8:49:22, a difference of
34 seconds.

I wonder if Bill or others have looked into such differences and
have an explanation as to why they occur. Just curious.