laser range finder's

Laser range finder’s, are used in C.A on the San Andreas Fault. Laser range finders are useful fore measuring the slightest movement between two points that are widely separated from each other. This is how it works two stations are mounted on the opposite side of a fault line. One station has a reflector. A pulse of laser light is sent to the reflector station, witch sends the pulse back to the sending station. The atomic clock is used to measure how long it took for the light to travel to the reflectors and back. Light travels at a velocity of 186,000 miles per second knowing that it is a matter of simple arithmetic to determine exactly how far the two stations are from each other. Weeks and months later additional measurements are made and if any movement along the fault has taken place to move the two stations closer to each other or farther than they where the time it takes for the laser pulse to travel back and forth will be different. The difference in the arrival times can be converted to a precise measurement of how far the land beneath has moved. Laser range finders can detect a change of only one fifth. I think that this is a good thing to have because one I like to know if the ground is moving two its kind of cool to know.(CH 4)