People who operate radars must choose the level of sensitivity needed for various weather conditions. They must also choose which tilt angle to aim the radar's scan. A common low-end tilt angle is one-half degree above the horizon. A higher tilt angle might be as much as two or three degrees, depending on the location and height of the precipitation that's being detected. The operator must also decide which radar image to observe and analyze, as there are several that can be displayed, from reflectivity (basic precipitation) and storm relative velocity (a wind profile) to VIL Density (an indicator of hail) and shear (a special display that isolates areas of especially large wind shear that can be useful in detecting potentially damaging winds.