Measuring fork rake - is there a trick?

Anyone know a reliable, reasonably accurate way to measure fork rake? Or am I on the right track eyeballing and dicking about with bits of string?

Put a decent sized, square (as in parallel) spacer on the back of the steerer tube. Place a long straightedge against this spacer. Measure the perpendicular distance from the straightedge to the dropout.

Rake = (distance from straightedge to dropout) - (spacer thickness - (0.5 x steerer tube outer dimension))

Or thats how id do it.

Thanks spuddy - sounds good.

Spuddy the Posty Boy turns into Rainman!!!

For a start its postie. And rainwhat?