A number
Palmer, the rudder gain is the amound of rudder angular movement for a certain amount of heading error. For instance if the rudder gain is set to 2 then for each degree of heading error(difference between the desired heading and the actual heading) then the rudder will be turned 2 degrees. If you set the gain to high the autosteering will swing wildly from port to stbd. If it is set two low then the auto head keeping will be less precise. The book has a pretty good explanation about how to set the ideal value. Incidentally the ideal value is speed dependent but for sail boats the speed range is not a big factor. I have a 30 ft spade rudder boat so I usually set my gain to 2. For different conditions I might move it up to 3 or down to 1.
