Pinecone
En-Route
The oil-pressure fired Hobbs tracks flight time, the hours a pilot can record in his logbook and what the FBO might charge for the airplane. The squat-switch triggered Hobbs tracks air time, the hours that count against the engine, its components, the airframe, and ADs.
Not exactly. FAA says you can log from FIRST MOVEMENT for the purpose of flight. So while taxi time counts, sitting running the checklist, warming up the engine, loading your flight plan before you move is not.
Engine, components, airframe, 100 hour inspections, and most service requirements are based on tach time. Not air time.