Recently, Jim Logajan posted:

"Neil Gould" wrote:
Thanks, and I understand the logic of your interpretation. It
clarifies the 50% notion that I've been taught, but it seems to make
the regulation rather pointless so long as there is some rationale to
the application of "pro rata" (for example, shares of ownership in
the aircraft or number of club members). If the FAA agrees with this
usage then the matter is settled! However, I'm still skeptical,
given the precedence of such as free ferrying to be considered
"compensation".

The following web page titled "Traps For The Unwary: Business Flying
And The 'Compensation Or Hire' Rule" discusses "pro rata" issues,
among others (such as the judicial invention of the "common purpose"
test):

http://www.aviationlawcorp.com/content/traps.html

This article does seem to embody some of my earlier notions of the
interpretation of this FAR. However, I think AirplaneSense's explanation
is more concise and precise than the article.

Neil