You spent hours to calculate the hour lines of your sundial, depending on the latitude of your location; then you calculated the angle at which the style should come in contact with the dial itself. Or you downloaded ready to print plans, http://planstomakeasundial.com so that you avoided all the trigonometric calculations. Whatever the case, at some point everything was ready. You just had to choose a sunny place in your garden to put your sundial.

Comes the great day. You read the instructions. Since they usually are one line long, they are pretty quickly read. Let's say you are in the northern hemisphere. You read: “Point the sundial to North” for a horizontal or an equatorial sundial (and their respective gnomon); “Make it facing South” for a vertical sundial; and “The reader, who is the gnomon, has to face North” for an analemmatic sundial.

You take your compass in hand... and are wrong.

The compass will guide you to magnetic North. To set a sundial, you must point to geographic North, “true” North.

Get up before noon and go out in your garden. Set up a long and fine stick upright. Make sure it is perpendicular to the ground and that its shadow is cast on a level ground. Mark the tip of the shadow. Measure the length between the stick and your mark. Rinse and repeat every quarter of an hour. At midday, the shadow must be the shortest, and then it starts stretching again.

When, during the afternoon, the length of the shadow is the same length as the first one your measured, draw a line between the two marks. Draw a perpendicular line: it points to true North.

If you want to set a vertical sundial, just spin 180° to find South.