If you use an instance of the control for the first time during runtime, there is no need to use Reset. But if you re-use the same control for showing a different chart in the same instance of the control without closing the form, where the control resides, you must call Reset before all other calls to the control. Because it doesn't hurt it might be a good practice to insert always a call to Reset at the beginnig of your chart creating routine, so you will not forget it, when you have to call the method.