The reference level of the MEP curve. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
Syntax
Remarks
 This property is used to retrieve the reference level of the MEP curve. If the curve is not in a horizontal plane, this value will be the start point's reference level.