Thanks Bill.
Googling, and back-tracking...
"...computed using the Darcy-Weisbach friction loss equation (which utilizes the Moody friction factor). "
from
http://sweb.uky.edu/~gvrajp2/jose/bpayne3.html
"Moody Friction Factor Calculator"
http://www.lmnoeng.com/moody.htm
in which:
"Calculation uses an equation that simulates the Moody Diagram"
So from
http://www.cam.org/~jacobie/faqonp~1.htm#q34
"3.5 What is the Moody diagram?"
A: A graphical representation of the Colebrook and the laminar flow equation.
and
3.8 What is the effect of pipe roughness on Friction Head?
The Colebrook equation gives the value of the friction parameter f with respect to the Reynolds number and the pipe roughness.
When the Reynolds number is small, below 2,000 (laminar flow region), pipe roughness has no effect at all. When the Reynolds number is between 4,000 and 50,000, that is low velocity and/or high viscosity, then the influence of pipe roughness is as equally important as the effect of velocity. When the Reynolds number is large, above 50,000, that is high velocity and/or low viscosity, then the friction is entirely dependent on pipe roughness.
WTF am I looking at? Need coffee...