Paweł Romaniuk has shared his workflow to take various parameters from a model, run the necessary algorithms and then write the area back to a parameter for use in a Revit schedule. Link to pdf download is below… Thanks Paweł.

UPDATED Download link:

Dynamo_Duct_Fittings_Calculation_V.0.1

Download:

https://www.dropbox.com/s/r1slk1sbo1eo971/Dynamo_Duct_Fittings_Calculation_V.0.1.pdf?dl=0

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Revit MEP Dynamo – Duct Fittings Calculation | LinkedIn