distances longer than 1200 ft (365 m), the target, if in proximity to the earth, may simply vanish into a mirage, caused by temperature gradients in the air in proximity to the heated surface bending the laser light. All these effects have to be taken into account. Calculation The distance between point A and B is given by where c is the speed of light and t is the amount of time for the round-trip between A and B. where φ is the phase delay made by the light traveling and ω is the angular frequency of optical wave. Then substituting the values in the equation, In this equation, λ is the wavelength ; Δφ is the part of the phase delay that does not fulfill (that is, φ modulo ); N is the integer number of wave half-cycles of the round-trip and ΔN the remaining fractional part. Technologies Time of flight - this measures the time taken for a light pulse to travel to the target and back. With the speed of light known, and an accurate measurement of the time taken, the distance can be calculated. Many pulses are fired sequentially and the average response is most commonly used. This technique requires very accurate sub-nanosecond timing circuitry. Multiple frequency phase-shift - this measures the phase shift of multiple frequencies on reflection then solves some simultaneous equations to give a final measure. Interferometry - the most accurate and most useful technique for measuring changes in distance rather than absolute distances. Light attenuation by atmospheric absorption - The method measures the attenuation of a laser beam caused by the absorption from an atmospheric compound (H2O, CO2, CH4, O2 etc.) to calculate the distance to an object. The light atmospheric absorption attenuation method requires unmodulated incoherent light sources and low-frequency electronics that reduce the complexity of the devices. Due to this, low-cost light sources can be used for range-finding. However, the application of the method is limited to atmospheric measurements or planetary exploration. Applications Military Rangefinders provide an exact distance to targets located beyond the distance of point-blank shooting to snipers and artillery. They can also be used for military reconnaissance and engineering. Usually tanks use LRF to correct the direct shoot solution. Handheld military rangefinders operate at ranges of 2 km up to 25 km and are combined with binoculars or monoculars. When the rangefinder is equipped with a digital