I recently purchased a portable sawmill powered by a 20 HP Honda 2 cyl gasoline engine. I placed an order for an hour meter/tachometer to keep track of running time for maintenance purposes. When I received the meter which just has an induction pick-up wrapped around the spark plug cable, is stated on the package that it was for one or two cylinder engines without an oil filter. Does anyone have any idea what the presence of an oil filter would have to do with the applicability of an induction hour meter? I am quite puzzled by this.