"Achterlieksverklicker".. So what do you call a telltale on the jib? "Vorsegelverklicker"?

Thanks for the numbers. Stalling the flow over any foil (like a sail) is pretty bad! So there you have the numbers Pete. Undersheet and you loose a bit, oversheet (stall the flow over the sail, or or not helming straight) and you are parked compared to those trimming it right.

Of course, undersheeting a lot is not fast either..