Hi Nicholas,
Thanks for contacting Syncfusion Support.
Regarding trackball closest point calculation
Since we have displayed the ChartTrackball based on nearest point calculation, the trackball label will be displayed on the nearest x-values (x-values provided in items source) of current mouse point.
For example, if the datapoints consist of 4 and 5 as x-values and if you are hovering the mouse over 4.49, then the trackball will be displayed on axis label value 4. If the mouse point is on axis-value 4.51, then the chart trackball will be displayed on x-value 5.
ChartTrackBallBehavior for larger data set
While using larger set of data, the datapoint are arranged closer. So, the chart trackball moves smoothly over the datapoints.
ChartTrackBallBehavior for smaller data set
For small set of datapoints, the distance among arranged data points are larger. So, the trackball does not move smoothly over datapoints and it is our current ChartTrackBallBehavior.
The above mentioned are current behavior of ChartTrackBallBehavior.
If we misunderstood you wrongly, kindly provide a demo sample with replication steps to reproduce your scenario at ours end and detailed information regarding the expected behavior. So, that it would be helpful for us to provide you a better solution.
Regards,
Devi