Hi Ronald,
If I understand you correctly, you want to know the position of the rudder at any time whilst at the helm by looking at some form of indicator?
Most of us (AFAIK) just mark each wheel with either three strips if electrical tape (or similar) at TDC when the rudder is set at directly straight, along with a piece of whipped on 2/3mm cord at TDC for feeling when using at night. You can get sophisticated rudder position gauges, mine has one as part of the AP system that shows position using a bar that shows red and green etc, but TBH, I use the wheel marks.