Our
flying club has "steam gauges" (no EFIS) and our tachs are "2300" RPM -- meaning not that they have an upper limit of 2300 RPM, but rather, when they are indicating 2300 RPM they "tick" at the same rate as a wall clock (or Hobbs). One of our planes used to have a 2400 RPM tach in it, so it was a little cheaper to fly than a comparable plane with a 2300 RPM tach (the club charges by the tach hour).
For pattern work, I think we typically see a tach time of around 15% less than what the Hobbs would be for that practice session. But on a long XC flight running at 2400 RPM, the tach time would end up being a little higher than Hobbs.
I've often wondered if the 25 or 40-hour Phase 1 testing was tach time or Hobbs time. Interesting post by Gil that it is [apparently] time in the air, and I don't know of *anybody* that tracks that time in their maintenance logs!
A dozen or so years ago I was investigating flying in Germany, and I learned that my U.S. pilot credentials were good over there (soon to change apparently!), BUT they would take 10% off my total time as shown in my log book, for anything that required a certain number of hours of experience. That's because over there, pilots are supposed to log ONLY the time they are actually in the air, whereas in the U.S., pilots log from the moment the plane starts moving under its own power, to the time it comes to a stop after landing (14 CFR 1.1), and most U.S. pilots simply log from engine start to engine shutdown, even though technically if you start the engine and sit idle for .2 hours getting everything all set up in the cockpit, you're not supposed to log that time. (Easy workaround: start the engine, taxi forward a couple of inches to test the brakes, then you can start the clock even if you need to remain stopped for a bit to set things up. Hehe.)
