On Sun, 9 Nov 2008 13:21:56 +0000, J. Clarke wrote
(in article ):

Clamp against the fence a straight board long enough that two points
on the work piece will ride on it. Cut one edge. You now have a
straight edge. Use that one against the fence to cut the other.

How do I get the first long board straight... ?

Do I need an even longer board?

How do I get THAT straight... ?

:-)