NavList:

Chuck V.,

The conclusions you draw from the now four photographs are interesting, regarding a possible further error in the sundial or its installation, beyond the gnomon alignment.

I notice that you derived in the past a formula that amounts to the Sawyer method, albeit for a different purpose.  When I was considering Frank’s “misaligned sundial”,  I could not come up with a formula for the error it would cause, and I fell back on a rather lengthy approach in Excel, using trigonometry in three dimensions and getting to the solution of the sundial error iteratively at each LAT / dec combination.  After Geoff Hitchcox then found the Sawyer formula, I was able to see that each point on my posted graph was within a second of time compared to that obtained from the formula.  If there is any interest I could post my trigonometry sketches to visualise what is happening in the sundial but my iterative calculation method would be tedious now compared to the speedy application of the formula.

Regards,

Adrian F.