Ben Jackson wrote:

If you then charge by Hobbs time there's a 'slop' factor in there
because Hobbs Tach. My question is: what is that factor? I was
hoping someone who had been involved in renting airplanes had an
estimate.

The FBO at the uncontrolled field at which I got my PPC used to use a factor of
1.2 times the tach in a Cessna 150. The aircraft had Hobbs meters, and we usually
paid according to the Hobbs, but sometimes one of the meters went TU.

George Patterson
Great discoveries are not announced with "Eureka!". What's usually said is
"Hummmmm... That's interesting...."