If you want to know there purpose of this, its going to be a speed counter, for measuring velocities. Basically, an oscillator (100khz+) is connected to the counter. There will be 2 barriers, the first will start the oscillator, and the second will stop it. Then the counter will display a figure via LEDs lit up. ie, 23. Then, using the distance between the barriers and this number, the velocity can be calculated. I expect real speed guns use a similar system, but this is for little things, not cars.