Interface for external servers implementing duct pressure drop calculation. 
   Namespace:   Autodesk.Revit.DB.Mechanical  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 17.0.0.0 (17.0.1090.0) 
  Since:  2014 
Syntax
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Remarks
 A typical way to use the external server can be: 
 - Implement a server class that derives from this interface
 - Create a new server object and register it with the service, see ExternalServiceRegistry .
 - Assign server for the duct pressure drop calculation in DuctSettings .