I have a Kestrel 5500. It's set to read Magnetic North, and I've calibrated the compass, out on a range - maybe 30 yards from any magnetic object. Once calibrated, holding it verticle and facing any given direction, the reading never stabilizes. It swings rather wide , sometimes as much as 20 degrees. For instance, if facing North (0), I get readings anywhere from 350 to 10. And it seems to display a fresh reading about every second. This can't be normal, can it? Has anyone else had this issue?