Ralph Weatherwax was found guilty by the court of speeding and assessed a fine of $35. He appealed to the Supreme Court, but that court transferred the appeal here on the grounds that the constitutional issues attempted to be raised had not been presented at the first opportunity. State v. Weatherwax, 607 S.W.2d 692 (Mo.1980).1
On this appeal the decisive issue is the failure of the patrolman to test the radar set at the site of the arrest and reasonably close to the time of the arrest. Reversed.
On December 4, 1978, Trooper Elliott of the Highway Patrol left his home at 7:00 A.M. to go on duty. While parked in his driveway, he tested his radar unit with two *35tuning forks and found it to be operating properly. Shortly before 11:00 A.M., the trooper was parked beside Highway 36 when he observed an automobile driven by Weatherwax and trained his radar unit on that automobile. His radar unit indicated a reading of 69 mph in a 55 mph zone. The trooper stated he had not tested the unit since 7:00 A.M. and did not test it at the site of the arrest. He did test the unit about 4:00 P.M. on that same day when he went off duty and found it to be operating properly.
James Smith, an employee of the Highway Patrol assigned to radar repair and certification, testified. Smith testified to the tests performed on radar units to insure their accuracy. Smith testified that outside influences such as power lines and neon lights can affect the readings obtained on the radar set used in this case. Smith also testified that the operation of a heater fan in the trooper’s automobile or the operation of two-way radio equipment could also affect the operation of the radar unit.
In City of St. Louis v. Boecker, 370 S.W.2d 731, 736[4] (Mo.App.1963) the court reversed a conviction because the city failed to show that the radar unit had been tested at the site and reasonably close to the time of the arrest. The court stated that there could not be the slightest doubt as to the requirement for the test at the site of the arrest and reasonably close in time to that event. The basis of the court’s ruling was the fact that outside factors can affect the operation of the radar unit as well as the fact that the unit can be affected by movement from place to place. At page 737[5] the court stated:
“But the requirement that proof be adduced that a radar speedmeter was tested and found to be operating properly at the site of and reasonably close to the time of an arrest should not place an undue burden on the prosecution, and should at the same time protect the rights of motorists against the possibility of error in this device which makes 'delicate measurements.’ State v. Graham, supra.”
The State, in its brief, concedes that Boecker requires testing of the radar unit at the site of the arrest and reasonably close to that time, but urges this court to overrule Boecker. This court has no inclination to announce a rule contrary to that in Boecker. This for the very simple reason that the scientific evidence presented in Boecker, and also in this case, shows that outside factors, such as power lines, can affect the operation of a radar unit. If the rule in Boecker were to be abrogated, then a radar unit could be set up in any location whether or not there were outside factors which would give an incorrect reading, and the prosecution would have no burden to show that the radar unit was operating properly at the site of the arrest. As stated in Boecker, State v. Graham, 322 S.W.2d 188 (Mo.App.1959) held that a radar unit is an extremely sensitive machine. As shown by the testimony in Boecker, and in this case, these units are sensitive to outside forces and must, therefore, be checked for accuracy at the site of the arrest. Further, as with any mechanical device, Smith testified in this case that radar units do malfunction. As stated in Boecker, supra, it is not an undue burden to place on the prosecution to adduce proof that the radar unit was operating properly at the site of the arrest and reasonably close in time to it.
Apparently, in an effort to overcome the failure to test the unit at the site of the arrest and reasonably close in time to that event, the State asked the trooper: “Based on your experience as a patrolman, as a driver, and your use of the radar device, did you also form an opinion as to the speed of this vehicle?” The trooper replied that by use of a combination of all three of those factors, he determined that the vehicle was traveling 69 mph. Because the radar evidence was inadmissible for failure to show that the unit was tested at the site of and reasonably close in time to the arrest, this opinion would likewise be inadmissible because the radar evidence was inextricably mingled with the other factors used by the trooper to determine speed.
It follows that the State failed to make a prima facie case when it failed to prove *36that the radar unit was tested at the site of and reasonably close in time to the arrest.
The judgment is reversed and the defendant Weatherwax is ordered discharged.
CLARK, J. concurs.
PRITCHARD, P. J., dissents in separate dissenting opinion.
. Weatherwax has filed a motion to transfer this case prior to opinion to the Supreme Court because a constitutional issue is involved. That contention has already been decided adversely to Weatherwax. The motion to transfer prior to opinion is overruled.