Sorry Rolf, I don't quite understand your concern...

When discussing mainsail twist with fellow catsailors, we've always talked about the sail twisting off so many inches (or feet). My understanding of this measure has been that if an imaginary line were extended through the head of the sail and out to the arc described by the boom, the difference between the intersect and the boom position gives the measure of twist in feet, inches, mm, whatever?

Have I been misunderstanding, misdescribing for the last 30 years?