Plots > Working with Plots > Markers and Callouts > To Add, Move, or Delete a Marker
  
To Add, Move, or Delete a Marker
1. Click inside an XY plot region.
2. On the Plots tab, in the Markers group, click Add Vertical Marker or Add Horizontal Marker. The marker appears on the plot.
* 
If you insert a second marker, it may overlap an existing marker. Move the new marker to see the marker below.
3. To move a marker, drag it to a new position.
Alternatively, click inside the marker callout and then edit the callout expression. Press Enter. The marker moves to its new position.
4. To delete a marker, click the marker line or click inside the marker callout. The marker is activated. Delete the callout value and then press Delete.
Alternatively, click the marker line or click inside the marker callout. The marker is activated. On the Plots tab, in the Markers group, click Delete Marker.
* 
• The callout expression can be any expression that evaluates to a real value. For example, you can insert the name of a variable that was defined above the plot.
• If the new position value falls outside the tick mark range, the marker jumps to the end of the axis and shows an error. You can drag it back into the axis range or change the callout expression so that its evaluated value falls within the axis range.