Re: Vector Compass problem 
>1)  occasionally the compass doesn't produce a clock signal until i reset
>it a couple of times.  any thoughts?

I have seen that too.  maybe have you main call comp_disable, do some
stuff, and call comp_init. It may fix the problem. The compass should
reset properly on it's own, but doesn't always.

>2)  it seems to be inaccurate by plus or minus 20 degrees.  what i have
>found is that 360 degrees is actually 360 degrees, but 90 degrees doesn't
>usually come up as 90 degrees. (i have the compass on a protyping board,
>and position it with the tiles on the floor to try and get 90 degrees)
>what happens is that the error alternates every quadrant.  so odd
>quadrants might be minus 20 degrees, but even ones plus 20 degrees.

Check you environment with a regular old compass, even a $0.49 you can
sometimes get at a drug store, or convenience store (the cheaper the
better, they are usually more affected by environment).  There is
re-bar in concrete floors that will affect a compass.  I have mine
over 9 inches from the floor for that reason.  Drag your compass
across the floor, if you see the needle wiggling, you are probably
passing near re-bar. 

Watch for screws and other metallic objects in your robot base. The
top of my robot has all aluminium screws, and velcro to hold
everything else on (including the compass).  Watch the aluminium, some
alloys have steel in them, I have some standoffs that seem aluminium
like, but definatly affect a compass. How far is the compass from the
motors in your base.  If it is too close (depends on motors) you will
probably get a wrong reading all the time. 


