Discrepancy in Relative Roughness Result

[Anonymous]

Hello, in a pressure drop post, author said Relative roughness (e)
is calculated as (e/D)= 0.00015 / 0.3355 =
0.00044709. while in another post, author said
Relative roughness (e) is calculated as D/e =
0.3355 / 0.00015 = 2236.67. Which formular is
the correct one? explain. Thanks

[Anonymous]

Link to post: knowledge.autodesk.com/support/revit-products/learn-explore/caas/CloudHelp/cloudhelp/2014/ENU/Revit/files/GUID-D1D409B3-41B2-4E19-8248-1117BED1A8C3-htm.html