Let P3 = PTerminal, be the instantaneous pitch at the end of the helix.
This value can be checked by converting the ending tangent angle, as previously described.
By reversing the values of sP and eP in the calculations, it is possible to easily calculate PTerminal, although it could get confusing.
Let sQ = eP, and eQ = sP So that Q1 = P3 (Q1 takes the roll of P1), and Q2 takes the roll of P2.
From the variable pitch equations:

Q2 = (N/(N-1)) * (eQ - sQ)/2 = (N/(N-1)) * (-1) * (eP - sP)) = -P2

Q1 = (L/N) - Q2 = (L/N) + P2
<<QED>>

To summarize the result, with the original sP and eP values, and the original variable pitch helix:

PTerminal = L/N + P2

I think that I will add a checkbox to the _VarPitchHelix script, to display the 4 additional pitches, P1, P2, Pinitial = P1, and Pterminal.

- Brian