Question about Hrv's Gamma diff scheme paper
 

Hi all, in Hrv's Gamma paper we have:

f_x=fN/PN, then the difference phi_f^{+}-phi_C can be written as:

phi_f^{+}-phi_C=f_x(phi_D-phi_C)

(where P is C and N is D), see attached figure. Nevertheless following the geometrical relationships I then to think that it must be:

(phi_D-phi_C)/PN = (phi_f^{+}-phi_C)/Pf

so that

phi_f^{+}-phi_C=Pf/PN (phi_D-phi_C)

Pf/PN != fN/PN, then I'm missing something...

How I can arrive to Hrv. expression?

Regards.

Any clues??

Regards.