Setting up the Equatorial Sundial and Reading the Time

The complete formula looks like this

Since 4(15TZ - Lat) is a constant (characteristic for each location) it can  be taken

care of  by rotating the equatorial dial around the gnomon by the corrsponding angle.

(As result the noon point will be at the bottom of the dial.) Thus we can use this simple equation:

                                          How to Find True North

In case of the equatorial sundial, finding north presents no problem at all:

You can use dial itself as a compass!  Put it on a horizontal surface and just turn it

(around its vertical axis) until the shadow of the gnomon indicates the current local

solar time. Calculate the solar time with this formula        

with:

ST     = Solar Time, i.e. the time the sundial should indicate

LT     = Local Time, i.e. the time that accurate local clocks show*

TZ     = Time Zone (negative west of Greenwich) [ -12 ...+12 ]

EOT = Equation of Time (negative when sun slow)  [minutes]

Lon    = Local Longitude (negative west of Greenwich)

*LT = UTC\GMT + TZ  where UTC\GMT = Coordinated Universal Time or Greenwich Mean Time

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(Pass: rainer)  Comments

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Various simple inexpensive sundials are presented at http://www.qwerty.co.za/sundials/howto/modeleqa.html

LT = ST - EOT + 4(15TZ - Lon)

LT = ST - EOT

ST=LT + EOT + 4(Lon - 15TZ)