Rhiannon,
If the Closure Stone was upright instead of being over 21" out of kilter like it is, the 'reading' would have been entirely different. I find it very difficult to believe that this most important and centralising orthostat was originally set in so much out of upright. In fact I know it wasn't because it has moved since last year! Look aound the remaining structure carefully and see how it is out of shape. Look at just the photos shown to see how the Capstone is way off centre to the main orthostat now and lurches badly to the left. I'll post a photo of the rear of the structure shortly to show you what I mean.

Local noon is when the sun reaches it's highest point daily, rather than any fixed 'time' of day set at the Greenwich Meridian.
The sun reaches it's zenith at a different time at any given location depending on how far east or west of this 'arbitrary' datum line.

I hope that makes it clearer.