It basically measures a distance by shooting a laser beam out to an object and measuring how long it takes that laser beam to bounce back. By knowing the speed of light (laser beam) and measuring the time, I think we can all figure out that the distance is computed by multiplying the time divided by two and multiplying it by the constant for the speed of light. Anyone that understands surveying realizes that to compute an x,y,z position, you need to know the distance to the object, the bearing (horizontal angle from a known line) to the object and the vertical angle (angle from gravity) to the object.