Laser ranging altimeters generally use two methods to measure distance: pulse method and phase method. The process of pulse method ranging is as follows: The laser emitted by the ranging instrument is reflected by the measured object and then received by the ranging instrument, which simultaneously records the time of the laser's round-trip. Half the product of the speed of light and the round-trip time is the distance between the distance meter and the object being measured. The accuracy of the pulse method for measuring distance is generally around+/- 1 meter. In addition, the measurement blind area of such distance measuring instruments is generally about 5 meters.