NavList:

I’ve been following the most probable position thread with interest, and it’s suddenly provoked something which I’ve never thought about before, and I can’t remember ever being warned against either.  I’m thinking particularly of something like a seven shot sandwich fix, when only two heights are calculated for a central time, and intercepts are averaged before plotting.  This ought to reduce random error, but what about the climbing and descending rate of the two stars concerned.  Most of the time, the rate of climb or descent should be roughly constant over a short period, so the movement will also be averaged.  However, what about when one star’s meridian passage coincides with time of calculation?  The average of the true heights of that star will be less than its true maximum height and more than its minimum height.  Should alarm bells ring if an azimuth comes out as 180 or 360, or can one say that for a short period around meridian passage height isn’t going to change much anyway?   Zn values of 180 and 360 do occasionally appear in AP3270/HO249 Vol1 but not often, heights around MP typically varying at a rate of 1 minute of arc per four minutes of time.  DaveP