POLICE USE THE DOPPLER RADAR GUN IN TRAFFIC SPEED CONTROL. THE GUN IS ESSENTIALLY A FREQUENCY-MEASURING DEVICE. THE BASIC PRINCIPLE OF OPERATION IS THAT THE GUN'S RADAR SIGNAL REFLECTED FROM A MOVING VEHICLE SHIFTS IN FREQUENCY BY AN AMOUNT DIRECTLY PROPORTIONAL TO THE SPEED OF THE VEHICLE RELATIVE TO THE GUN. TYPICALLY THE GUN IS CALIBRATED BY PLACING IN FRONT OF IT A VIBRATING TUNING FORK, WHICH PRODUCES A REFLECTED SIGNAL TO WHICH THE GUN RESPONDS AS IT WOULD TO A MOVING VEHICLE. TO BE CERTAIN THAT THE RADAR GUN WILL PRODUCE ACCURATE SPEED READINGS, IT IS NECESSARY TO VERIFY THAT THE FREQUENCY OF BOTH THE GUN'S RADAR SIGNAL AND THE TUNING FORK ARE CORRECT WITHIN ACCEPTED LIMITS. THE PROCEDURE FOR CHECKING THE FREQUENCY OF THE GUN'S RADAR SIGNAL INVOLVES CARRYING THE GUN IN A MOVING VEHICLE EQUIPPED WITH A CALIBRATED SPEEDOMETER, POINTING THE GUN AT A STATIONARY OBJECT, AND COMPARING THE GUN'S READING WITH THAT OF THE SPEEDOMETER. THE PROCEDURE FOR CHECKING THE TUNING FORK'S FREQUENCY INVOLVES TESTING THE FORK AGAINST THE STANDARD TIME AND FREQUENCY BROADCASTS (RADIO OR TELEPHONE) OF THE NATIONAL BUREAU OF STANDARDS (NBS). A PILOT PROGRAM TESTED 200 FORKS IN COLORADO AND WYOMING BY MEANS OF THE NBS BROADCASTS. THE PROGRAM FOUND THAT THE TUNING FORKS WERE VERY RELIABLE. POLICE AGENCIES FOUND THEY WERE ABLE TO SAVE SUBSTANTIAL LITIGATION COSTS BY PRODUCING NBS-TRACEABLE CALIBRATION CERTIFICATION FOR THEIR RADAR EQUIPMENT. A QUESTION-AND-ANSWER SESSION THAT FOLLOWED THIS PRESENTATION IS DOCUMENTED. (LKM)