This is the one precise, foolproof way to calculate true south where your house or business is, and you can do it for free. The closer you are in time to the winter solstice (December 21 in the northern hemisphere, March 21 in the southern), the easier it will be to conduct this procedure, and you’ll need to do it on a bright, sunny day.
To make this work, start with a visit to Weather Underground and enter your zip code in the search box. Then look for the hyperlink that says “Sun & Moon.” When you click on it, you should see a table entitled “Astronomy.” The first item on the list should be “Actual Time,” and the middle column should be “Solar Noon.” That is the time in your zip code at which the sun will be coming from due south today. About 15 minutes before solar noon, position a plumb bob in full sun, hanging from a stationary pole or other elevated support and hanging to within a couple of inches of the ground. We use our tractor’s front-end loader bucket for hanging, which is ideal. The extra time is to give the plumb bob a chance to become completely stationary before Solar Noon arrives. At the moment of Solar Noon, trace the shadow the plumb bob casts on the ground. The line you trace runs exactly north and south.