Article 3 Prescribed device
The following device is prescribed for the purposes of Article 23 of the Road Traffic Offenders (Northern Ireland) Order 1996, that is to say, a manually activated device designed or adapted for recording the measurement of the speed of a motor vehicle (“vehicle A”) from another motor vehicle (“vehicle B”) by—
measuring the time taken by vehicle A to pass two positions on the road either directly or by reference to the time taken by vehicle B to pass the same two positions on the road;
recording the distance between the two positions by counting the odometer pulses from vehicle B as it travels between the two positions; and
calculating the average speed of vehicle A over the distance between the two positions by reference to the time recording in paragraph (a) and the distance either calculated in accordance with paragraph (b) or measured manually.