Hobbs time isn't necessarily the time the engine is running ... the Hobbs can be switched on by various things, the master switch, speed sensing, squat switches etc.
In a 172 I don't know specifically what starts the Hobbs turning but I have been told it only records actual flight time (I suppose whether it measures take off and landing roll or not is rather moot). For all I know it may vary from one aircraft to another (age related or factory related.)
I log start of taxi to end of taxi (movement under own power). I get charged Hobbs + 0.2.
What I log and what I pay seem pretty closely aligned to me so I guess what I say in para 1 . is about right.
I am too old and ugly to be counting hours for another license so I have no reason to try and exagerate.
Last edited by Dave Gittins; 26th April 2012 at 11:33.