Open the circularGaugeDemoWPF project in the customcontrol that you downloaded from this site.
Remove the 4 controls from the Window1.XAML.
Remove the code from the window1_loaded event in codebehind.
Add using CircularGauge;
Add to constructor:
CircularGaugeControl cg = new CircularGaugeControl();
cg.MaxValue = 500;
cg.MinValue = 0;
cg.Radius = 100;
cg.ScaleLabelRadius = 80;
cg.ScaleStartAngle = 300;
cg.ScaleLabelFontSize = 12;
cg.DialText = "RPM";
cg.PointerThickness = 9;
cg.FontSize = 10;
cg.ScaleStartAngle = 140;
cg.ScaleSweepAngle = 200;
LayoutRoot.Children.Add(cg);
This is not a copy from your code!
This works on my station.