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The attached graph shows thoughts on the possible errors given by a spherical sundial if it had been installed with its gnomon inclined at an angle of 48.64 degrees, on a dial located at a latitude 41.36 North (Frank’s post of 30th May).

Each point on the graph came from an iteration exercise to determine where a shadow from the tilted gnomon would intercept the tilted hour-circle.  I’ve never done something like that before so I’m hoping the method is valid.  The graphs are limited to four declinations of the sun (all positive declinations) and hour angles of up to 75 degrees either side of solar noon.

Thank you to Frank for posting the photos of the times indicated by the two sundials at Mystic (5th June post). My assessment of the errors in the two dials is similar to that of Geoff Hitchcox (post of 10th June), my figures being as follows :

Photos taken from 14:09:10 EDT on 26 April 2024 :
  Armillary dial photo  :
  True LAT of sun = 13h 23m 39s, True hour angle of sun =  20.91 degrees.
  Time indicated by dial = about 13h 32½m
  Error against LAT = about +9 minutes

  Vertical dial photo :
  True LAT of sun = 13h 24m 59s
  Time indicated by dial = about 13 h 24 m
  Error against LAT = within about a minute

Photos taken from 16.35.30 EDT on 28 April 2024 :
  Armillary dial photo  :
  True LAT of sun = 15h 50m 17s, True hour angle of sun = 57.57 degrees.
  Time indicated by dial = about 16 h 01½ m
  Error against LAT = about +11 minutes

  Vertical dial photo :
  True LAT of sun = 15h 51m 37s
  Time indicated by dial = about 15 h 49 m
  Error against LAT = within about 2-3 minutes

The other page attached is to do with the effects of using the wrong latitude in a time sight (if I’ve used Franks equations for the LHA correctly, 8th June post).

Regards,
Adrian F