During a scan the antenna of the radar performes at a few elevations (tilting with respect to the horizontal plane) a full turn about his vertical axis (azimuth). To be more accurate, the azimuth is the clockwise angle of the radar antenna with respect to the direction of North. At every position of the radar antenna the reflectivity is measured as a function of the distance. All information together delivers a view of the three-dimensional distribution of reflectivity in the atmosphere.

The KNMI radars perform a small scan over just 4 low elevations every 5 minutes and a large scan over 14 elevations up to 12 degrees every 15 minutes. The well-known radar precipitation images are just a horizontal cross-section at constant altitude above the earth surface through the three-dimensional data of the small scan. These precipitation images are actually called pCAPPI's, or pseudo-Constant-Altitude Plan-Position Indicator. An example of such a pCAPPI product can be viewed on this page.

By adding all 288 pCAPPI-images of one day, running from 8 to 8 UTC, the accumulated precipitation can be calculated.