The stereograms produced so far have been sketches, sufficient to force us to think about how the projection works but not accurate enough for serious applications.

For geometrical constructions in two dimensions a ruler and protractor are the essential tools. Examples of the constructions are:

1. (a) drawing the line which passes though two points;

2. (b) measuring the angle between two co-planar lines;

3. (c) drawing the line which bisects the angle between two lines.

In three dimensions the equivalent constructions are:

1. (a) finding the plane which contains two lines;

2. (b) measuring the angle between two lines or between two planes;

3. (c) finding the line which bisects the angle between two lines or the plane which bisects the angle between two planes.

The stereographic net (stereonet) is the device used for these constructions. It can be thought of as a spherical protractor and ruler rolled into one. The stereographic or Wulff net is shown in Figure 9c. The net is a reference stereogram consisting of pre-plotted planes. The net in Figure 9c, an equatorial net, shows many plotted great circles representing a family of planes, sharing a common strike but differing in their angle of dip. These planes can be envisaged as those obtained by rotating a protractor (Fig. 9a) along its straight edge (Fig. 9b). The ticks along the protractor's circular edge denote lines spaced at constant intervals within the plane of the protractor.