Re: Trim gauge question.
It probably doesn't mean anything because in my experience the gauge sender isn't set where it should be. They usually just get it close, tighten up the bolts and as long as it works it's good. Takes a few minutes of time to do it right.
If it's a Mercruiser, it's easy to adjust the gauge so the pointer is where it should be. Not familiar with Volvo's. Note where the gauge is when the boat is running like you want it to on plane. With the boat out of the water, set the drive so the pointer is at the same place it was when the boat was running in the water. Loosen the two screws on the trim gauge sender (on the gimbal ring) and turn the sender until the pointer moves to the marks. You probably won't have to move it very far. Tighten the bolts back up.
Best trim will change slightly depending upon boat loading, water conditions, etc. But at least the gauge gives you a quick reference to where the trim is.