The device shoots out a laser beam straight to the area of interest, then it reflects back to the rangefinder. This is why reflective surfaces do much better than non-reflective. The greater the distance, the longer it takes to get back the range data. For the most part high end LRF can measure within half a yard. A good rangefinder shoots out laser beams rapidly and interpolate the data and give you the best reading, so scan speed matters in an rangefinder especially for extreme long ranges. How accurate the reading is depended on how you're focusing with the reticle. Usually tree branches, rain drop, fog or leafs can affect the beam. Other times insufficient battery also don't provide much juice for the LRF to work well.