My Beneteau Oceanis 390 Tula has an Autohelm ST4000+ fitted. The heading on the helm display is way off from the readings on my two GPS's and my main steering compass which coincide nicely. The manuals for the Autohelm were apparently lost overboard by a previous owner one dark night after an extreme amount of partying. Don't ask me the facts, they sound way too scary. Any ideas as to how I can swing the Autohelm compass to the proper heading? A friend told me I need to motor in circles and adjust something. He was not sure what.