[Rhodes22-list] Compasses

[Bill Effros]

Slim,

 From comments sent previously, you can infer the problems manifest in 
all compasses: they will all kick out numbers, but there is no fixed 
relationship between any two numbers until you discover what that 
relationship is.

Let's start with your compass.  First rotate it 360°, slowly.  Is it 
capable of stopping at any number?  If the magnet has been badly 
damaged, it will jump over some numbers, no matter which way you point 
it.  If that's the case, you will not be able to use this compass 
because you will never be able to find another compass that makes the 
same mistakes in exactly the same way.  Consistency is the critical 
function of any compass.

Assuming that your compass is capable of pointing in 72 different 
directions (5° intervals) you must next determine if it is consistent.  
Point the compass so it reads 0°.  Make a line in the sand.  Turn the 
compass 180°, and write down what number the compass points to.  Turn it 
back to 0° using your line in the sand.  Does it say 0°?

Please note, if the compass is working properly, the compass card should 
not move at all -- only the housing and the board you may have mounted 
it on should move.  It may not be pointing in a predetermined direction, 
but it should be pointing in the same direction all the time.  That's 
the way properly functioning compasses work.

Using a protractor, draw a line in the sand at a 90° angle intersecting 
your first line.  Put your compass on this new line, first one way, then 
the other.  It should read 90° and 270°.  If it doesn't, you've got a 
problem.  Make more lines at 45° angles.  The compass card should not 
move.  Your computed angles should equal what you see on your compass.

If they do not, someone may have "corrected" your compass.  The 
adjusting magnets, built into the housing of your compass, must be 
pulling your compass card in different directions as you rotate the 
housing around your compass magnet. Try to twiddle with them, so that 
they don't change the orientation of your compass card when you rotate 
them around.  If you can't make this happen, it's time for a new compass.

If your compass is consistent, it's time to mount it on your boat, and 
figure out what direction it's actually pointing.

Timid Virgins Make Dull Companions.  Lesson II.

Bill Effros