The outside circle is relative target bearing. 302 this goes in the TDC.
The inside circle is true bearing. 235 this can be used on the map for plotting...
The ruler tool helper is in true bearing. Start the ruler on your sub and when the line goes through 235 you have the bearing. Using true bearing for plotting takes less steps and introduces less error into your plot.
But the TDC still NEEDS the relative bearing !