An old and heavily used 70 cm Deboichet R12 has been raked 4 cm forward (the fin can now be labeled a R12 Rake +4). The red arrows show places on the fin head with new material put on (epoxy putty is most often OK), and the blue arrows show places, where some original material has been removed.
The yellow arrow indicates the rotation point for the raking forward - and with a little imagination it's easy to understand that this particular fin shall violate the formula rule saying that the max. length of a fin is 70 cm - unless, of course, a little material shall be removed from the tip of the fin.
From : http://www.peterman.dk/start-windsurfing-gb01.htm