On Mon, 2 Jul 2007 16:35:20 -0400, "Peter R."
wrote:

On 7/2/2007 3:31:14 PM, Orval Fairbairn wrote:

Sometimes, unscrupulous owners will wire the Hobbs to the master switch,
so you get charges whenever the MS is ON.


Isn't that true for the Hobbs installed by the aircraft manufacturer in newer
aircraft? I was taught that all the newer model C172s' Hobbs are wired to the
master, which results in about a 20% greater difference between their
readings and the tach.

The new 172,182,206 are all activated by oil pressure not the master
switch.