NavList:

John Howard, you wrote:
"When I do a set of sights around noon I record the max Hs (and time)."

Suppose the hang time (the period when the altitude scarcely changes) on some date at some location is five minutes. We know from prior calculation that the Sun's altitude will not change by a measurable amount in that period. Suppose in a two-minute period centered on the middle of that hang time you took the following altitudes of the Sun every 30 seconds:
  41° 29.4'
  41° 29.6'
  41° 29.1'
  41° 30.2'
  41° 29.3'

These are not unreasonable observations, but on the date in question at this latitude, the altitude should not even change by 0.1' during this period. What would you use for your noon altitude? Plot these altitudes. I think you can see that the maximum could easily be a statistical fluke --a little noise in the observation process. We shouldn't necessarily go with the maximum observed value. An option here would be to average the lot. That gives 41° 29.5'. There are other options when more sights are available. 

Frank Reed