The MagnetoSpeed does not have any use for me. It will only measure speed at the muzzle and, on most rifles, it will shift the point of impact. I used to use an Oehler and now use a Steinert Superchrono. It does not read subsonic speeds but I am not into bows and air rifles. After shooting several hundred shots, including shotguns over it, it has given no error readings and it is the only chronograph that I feel confident enough to measure speed at 500 metres.