Folks,
With our "ever changing" rules, two of the things that have been constant are the definitions of (loosely described) "Chock to Chock" for logging pilot time, and "time in service" for maintenance purposes, wheels off to wheels on.
Thankfully, these definitions, in my experience, are universal.
Lead Balloon has spelled it out in legal terms.
If you are being told otherwise by your instructor/CFI/LAME/FOI/AWI/whatever, they are airing their ignorance, the correct aeronautical term being: "talking bollocks".
Commercial organisations can arrange their billing on whatever basis they choose, it doesn't have to be related to Flight Time or Time in Service, or tacho time, dreamtime or whatever.
And confirming, VDO and Hobbs a the name of instrument makers, as are Smiths, Stewart Warner (for the older brigade) and the dreaded Lucas.
Tootle pip!!
PS: Many "tachos" that are part of a rev counter only record "time" at the same rates as your watch at a reference RPM, if you'r using higher RPM the recorded time will be more than elapsed/chronological time, at low RPM, they will record less than elapsed time.
Last edited by LeadSled; 13th Apr 2018 at 14:03.
Reason: typo