This sample depicts the trackball behavior in the chart. To view the trackball and its tooltip, hover over the chart or tap on it in touch-enabled devices.
The trackball is used to track a data point close to the mouse or touch position. The trackball can be enabled by setting the Enable property of the crosshair to true and the Shared property of the tooltip to true in the chart.
More information about the trackball can be found in this documentation section.