$author = "Walt " ;

I think you have it backwards. First you have to recognize a shift and
*then* tack, if appropriate. If you're really good, you'll see the
header coming and tack before it gets to you.

Actually, it pays to sail a little into the knock before tacking. Granted
you still need to assess whether the shift is persistent enough to tack on,
but it pays to hold off on the tack until you have seen at least 50% of the
heading change.

cheers
Marty