
Quoting
Trooper Operator's Manual (page 11)
Acquiring and displaying valid target (and patrol) speeds requires obtaining a proper tracking history, as described below:
1. Visually observe target vehicle and estimate its speed. Recheck antenna aim and MOVSTA selection. Observe other vehicles which may be in the radar beam and which are potential targets (or may block the radar's "view" of the selected target), especially those which are larger, closer, or much faster than the selected target. Be alert to terrain or roadside features, which can cause interference, incorrect readings, or display blanking. (Such features include power lines, radio/TV transmitters, bridges, guardrails, and other large reflectors, etc.)
2. Listen to the Doppler audio. The pitch of the tone should correspond to the visual estimate made above. The tone should be clear and strong; scratchy, “buzzy”, or garbled tones could indicate interference of some sort.
3. Check the radar TARGET display. The reading should closely match the visual estimate and the pitch of the audio tone.
4. If you are operating in Moving Mode, check your speedometer against the PATROL display. The readings should correspond. Discrepancies indicate the radar is reading the PATROL speed incorrectly, and thus displaying an incorrect TARGET speed.