This is really interesting with respect to a thread about a magneto-something or other velocity measuring tool, (vs. a chronograph) which some fire members have said degrades accuracy....
If I'm understanding you correctly, you're speaking of the MagnetoSpeed chronograph. The sensing technique used by the device has nothing to do with influencing accuracy, it is due to the fact that you've got something hanging on the barrel near the muzzle interfering with normal vibration patterns.