I've got a reasonably new Raymarine ST 4000 autopilot. It worked fine when first installed about a year ago but soon thereafter developed a problem. When you press the -1 and -10 buttons simultaneously, it should cause the boat to auto tack to port. Conversely, when you press +1 and +10 simultaneously, it auto tacks to starboard. Well, it does it just fine going to port but nothing happens going to starboard. I've taken the unit out and had it bench tested. The results were just fine. It auto tacked to port on the bench without problem. Any idea why it wouldn't do it on my boat? Could it be the flux gate compass? Otherwise, the unit works absolutely fine. For example, I can press -10 and it will adjust course 10 degrees to port. Or I can press -10 nine times and it will allow me to tack to port. It's haunted.