A button compass can be used to verify the operation of a primary compass.I have seen people swear that their compass was broke because they knew that it was "that direction".When you have two things saying north is that way it makes it easier to admit you're wrong.Then again if it is 9:00am and both your compasses are pointing at the sun,you could be standing on an iron deposit.It happened to me.....


BOATMAN
John