How much difference in heading/bearing between consecutive legs is "officially" considered a turn? While examining FAA's TERPS manual (Order 8260.3D) and PBN manual (Order 8260.58A), I noticed two seemingly contradictory statements.


  TERPS 8260.3D Chapter 14. Departure Routes, 14-3-4 . Construct turning segments when the course change is more than 15 degrees


(emphasis mine)

Whereas in PBN manual, it seems that a deviation of 10 degrees is considered a turn.


  PBN 8260.58A 1-2-5,b,(1)a . [...] Not applicable for FB turns of 10 degrees or less.


(emphasis mine)

Am I missing something. Is there any consistent rule that states when a transition between legs of an Instrument Procedure is considered a turn or a straight flight?
I will have to answer my own question, since I have noticed that in FAA's PBN Manual it states:


  PBN 8260.58A 1-2-5c . Turn parameters. For OEA construction, a turn is indicated when the course change exceeds the alignment tolerance of 0.03 degrees.


So, at least as far as route design is concerned, the alignment threshold for turn indication is 0.03 degrees.