Call me old fashioned, or just plain stupid but I measure my mast rake between the bottom of the forestay and top of the bridle. Its very quick and easy to adjust. I also think that the new fat/square top mains don't require as much mast rake as the older designs but again I'm not a sailmaker and have no means to prove this theory. For me I just feel the boat settles in the groove quicker and for longer with minimum rake.