What is a Hobbs meter?

A Hobbs meter is an hour meter that counts clock time while an aircraft's engine runs, usually started by oil pressure or the master switch, depending on how it's wired. Operators use Hobbs time to bill flying and to time maintenance, because an hour on the meter is an hour on the clock.

How RALPH handles it

In RALPH a Hobbs meter is one kind of meter an aircraft can declare, alongside tacho, engine and collective hour meters. Each aircraft carries only the meters it really has, under the labels your operation uses. Every logged flight records a reading for each of its meters, and a meter’s reading comes from its trail of flights and audited adjustments, such as an opening reading or a replaced meter, so every reading can be traced to the flight or adjustment behind it.

Questions, answered

Is Hobbs time the same as flight time?
No. A Hobbs meter usually runs from engine start to shutdown, so it includes taxiing and ground running, while flight time in a pilot's logbook is counted by its own rules.
Why is Hobbs time more than tacho time?
A Hobbs meter counts every minute the engine runs, while a tacho counts slower at low RPM, so on the ground and at low power the Hobbs gets ahead.