sail shape

i reacently read a book about sail shape and how to record it

you take a pic of the sail from the underneath and from the picture you 1)mesure the distance across the sail then 2)measure the distance to the point of most depth in the sail

show 2 as a percentage of 1

then measure the distance of the point with the most depth of the sail to the centre line show this as a percentage of 1

then you write down in your log book for example

sail shape 1- most depth 40%
distance from centerline 20%

does any 1 know what depth works best in a mirror

chris rust (legend)