A constant line label shows information on the constant line. You can configure label appearance using the label object. Within this object, you can set font options, a position and text using corresponding fields. In addition, you can specify the horizontal and vertical alignments for the label.
You can set the label options for all the value axis constant lines together. For this purpose, use the valueAxis | constantLineStyle | label object. Note that the options that are set within the valueAxis | constantLine | label object override the corresponding options that are set within the valueAxis | constantLineStyle | label object.