The TooltipVisibility property must be set to Visibility.Visible if you want to show the tooltip. The tooltip displays the X and Y value of the current mouse location. Since the Y-value depends on theY-axis and multiple Y-axes are possible, you have the FallbackTooltipAxis property to specify exactly which Y-axis the tooltip is bound to.
The tooltip has cuztomizable background - use FallbackTooltipBackground to set the Brush.
