I understand how a tach runs, or atleast how my tach runs. In this case (and I believe all cases?) the tach is always running reguardless of engine speed, however the SPEED it runs out varies with RPM (household electrical meter good analogy) ranging from very slow operation at idle/taxi RPMs increasing as RPMs are increased. Hobbs (generally) run on oil pressure, which is also always present when an engine is running, however the rate it runs is calibrated to TIME rather than RPM like the tach.
I always thought that Tach would be lower than hobbs time, so I was surprised to find my tach time consistantly higher than what a hobbs, if installed, would be reading. All my flying is cross country, usualy in the 2-4hr range with cruise rpm of 2500or2550RPM, which means that the RPM is running close to (or even faster than) true time. I suppose the "Tach<Hobbs" I see/hear all the time comes from flight instructors who operate much more commonly at low or even idle power settings.
I'm really just looking for an easy way to track my logbook time. Unfortunately in the airplane I'm already keeping track of flight time (wheels up to wheels down) for CC planning purposes, time duration on each fuel tank, IFR Approach/Hold Timing, and I would prefer not to start a timer for engine start/shutdown as well.