It depends on the quality of the rangefinder, but generally the accuracy tolerance is substantially better than +/- 50m, more like +/- 1m or usually better. It's an optical physics thing really. The problem with lower quality rangefinders is that the further out you go, the more it requires good environmental conditions and target surfaces normal to your line of sight with highly reflective materials. The average rangefinder will nail steel targets out to 600m with ease, but have a hard time ranging a small wooden stump next to it or a bush (yeah, forget that). The mil-grade rangefinders can pretty much be pointed at a grassy knoll at 2000m and still give you an accurate measurement.