The recommended way to manage markers is Worksheet#add_chart Markers are created for a two cell anchor based on the :start and :end options.
The Marker class defines a point in the worksheet that drawing anchors attach to.
Creates a new Marker object
The column this marker anchors to
The offset distance from this marker's column
shortcut to set the column, row position for this marker or an Array. String or Array.
handles multiple inputs for setting the position of a marker
The row this marker anchors to
The offset distance from this marker's row
Serializes the object