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It is essential to find true south using the solar noon shadow method. Working out true solar noon is however a complex problem involving variations in the earths orbital speed amongst other things. Fortunately there is a website www solar-noon.com that will calculate a full years printable table of solar noon times for your geographical location. To do this you will need to find out your exact geographical coordinates first from a gps or smartphone app.
I used this table to, on three days (not consecutive due to cloudy weather), mark the true south shadow line which I then scribed permanently into my concrete driveway.
If you are able to leave your tripod legs spread and fixed between uses, it is just a matter of placing the front leg precisely on the scribe line and using a straight edge across the back legs and a carpenters square to precisely set the back legs at right angles to the scribe line.
Works every time although I now use a polemaster to refine my precise alignment.
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