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The law regarding these devices as a means for testing speed is found in 75 Pa.C.S.A. Section 3368. The law is set forth below:
75 Pa.C.S.A. § 3368 Speed timing devices
CHAPTER 33. RULES OF THE ROAD IN GENERAL
SUBCHAPTER F. SPEED RESTRICTIONS
(a) Speedometers authorized.--The rate of speed of any vehicle may be timed on any highway by a police officer using a motor vehicle equipped with a speedometer. In ascertaining the speed of a vehicle by the use of a speedometer, the speed shall be timed for a distance of not less than three-tenths of a mile.
(b) Testing of speedometers.--The department may appoint stations for testing speedometers and may prescribe regulations as to the manner in which the test shall be made. Speedometers shall have been tested for accuracy within a period of 60 days prior to the alleged violation. A certificate from the station showing that the test was made, the date of the test and the degree of accuracy of the speedometer shall be competent and prima facie evidence of those facts in every proceeding in which a violation of this title is charged.
(c) Mechanical, electrical and electronic devices authorized.--
(1) Except as otherwise provided in this section, the rate of speed of any vehicle may be timed on any highway by a police officer using a mechanical or electrical speed timing device.
(2) Except as otherwise provided in paragraph (3), electronic devices such as radio-microwave devices (commonly referred to as electronic speed meters or radar) may be used only by members of the Pennsylvania State Police.
(3) Electronic devices which calculate speed by measuring elapsed time between measured road surface points by using two sensors and devices which measure and calculate the average speed of a vehicle between any two points may be used by any police officer.
(4) No person may be convicted upon evidence obtained through the use of devices authorized by paragraphs (2) and (3) unless the speed recorded is six or more miles per hour in excess of the legal speed limit. Furthermore, no person may be convicted upon evidence obtained through the use of devices authorized by paragraph (3) in an area where the legal speed limit is less than 55 miles per hour if the speed recorded is less than ten miles per hour in excess of the legal speed limit. This paragraph shall not apply to evidence obtained through the use of devices authorized by paragraph (2) or (3) within a school zone or an active work zone.
(d) Classification, approval and testing of mechanical, electrical and electronic devices.--The department may, by regulation, classify specific devices as being mechanical, electrical or electronic. All mechanical, electrical or electronic devices shall be of a type approved by the department, which shall appoint stations for calibrating and testing the devices and may prescribe regulations as to the manner in which calibrations and tests shall be made. The certification and calibration of electronic devices under subsection (c)(3) shall also include the certification and calibration of all equipment, timing strips and other devices which are actually used with the particular electronic device being certified and calibrated. The devices shall have been tested for accuracy within a period of 60 days prior to the alleged violation. A certificate from the station showing that the calibration and test were made within the required period, and that the device was accurate, shall be competent and prima facie evidence of those facts in every proceeding in which a violation of this title is charged.
(e) Distance requirements for use of mechanical, electrical and electronic devices.--Mechanical, electrical or electronic devices may not be used to time the rate of speed of vehicles within 500 feet after a speed limit sign indicating a decrease of speed. This limitation on the use of speed timing devices shall not apply to speed limit signs indicating school zones, bridge and elevated structure speed limits, hazardous grade speed limits and work zone speed limits.