A constant line is a straight line that extends over the entire chart and indicates an axis value. Constant lines are always perpendicular to their axis.
Use an axis's BootstrapChartAxisSettings.ConstantLineCollection collection property of to configure its constant lines. A BootstrapChartConstantLine class object represents each constant line the collection. Use its properties to configure the constant line's value, label, and presentation. The BootstrapChartConstantLine.Value property should be set for a constant line to appear on the chart.