@ktorn even better, using the wind as a helmsman. A compas just tells you what direction you are heading, the helmsman keeps you going in that direction.

The wikipedia page is pretty good, particularily the history section: https://en.wikipedia.org/wiki/Self-steering_gear

Also this article is good, http://www.faymarine.com/plansite/fay_marine_yacht_pl.htm (although unfortunately it complete avoids discussing the most interesting part, negative feedback to prevent oscillation) It covers the 4 most common configurations - but note that my trailing servo style isn't described - I have never seen or heard of anyone using this style, so it might be my invention!