How to set the chart date and time range.
The chart has two TDateTime properties, StartAt and EndAt, that govern the displayed date/time range. If you set the values of these properties individually, there's the danger that at some point the value of EndAt will be before the value of StartAt. If this happens, the chart will throw an EssBadValue exception. Using the SetDateRange method avoids this problem, as it allows you to set both properties in one step.
When you set the chart date range, you're setting the initial display date/time span. If the racAllowDragScroll option is enabled, the user is able to "grab" any blank part of the plot area, and drag the chart left or right, and this will change the values of the StartAt and EndAt properties correspondingly.