This diagram explains the operating principle of the confocal microscope. At each of 180 points, white light is shone through a series of lenses which split the light into constituent wavelengths such that different wavelengths focus at different heights in the probe's range. When a surface is placed in the probe's focal range, the light that is incident, reflects off the surface, is gathered and analyzed. By analyzing the intensity of the wavelengths in the collected light, the probe can detect which wavelength of light was in focus on the surface and from this can calculate and output the height of the surface.
The image is a plot of the data measured by the probe on the scanning machine. The probe measures and reads out the height of a surface in its range at 180 points on a line 1.8mm wide. This plot results from measuring a 1.8mm line on a cylinder. The groove intersects the line several times as it winds around the cylinder and so shows up as several crescent shaped dips in the height of the surface.
This method is meant to illustrate how data collection works for a cylinder. During acquisition, individual measurements of the height at 180 points along a line are taken in quick succession, at slightly different positions, as the cylinder rotates, and then stitched together in analysis software.