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I got a reply from Tom over in tech groups and his response appears to link with Andrew's indication of using UTC only.
I did not think of this because my brain was assuming that Gemini was relying on the local time to work out object locations.
By entering UTC and a timezone of 0 removes issues like daylight saving, +'s and -'s etc. So Gemini must calculate the observer's location objects from the longitude starting from UTC.
This makes sense and far more accurate.
This question really began in my mind back when I had a LXD55 Autostar where I would enter my co-ordinates and local time. Then slewed to a bright star and noted its position. Then I would repeat the exercise using the same co-ordinates but then recalculate my local time by simply extrapolating from UTC the longitude as a ratio of 12hrs (eg when I was in living in Yarraman at the time ~151East, so I would add 12 x 151/180 onto the UTC and enter that in my time). Then I would slew to the same object and remarkably the position was closer to the centre. Ie Autostar at the time appeared to use local time in its calculations somehow!!!
A long and interesting observation.
Darrin...
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