You have the Hobbs type meter. These have been used for many years in aircraft and tractors as well as many other types of equipment.
Most will say that rated speed is necessary to get one hour's use in one hour. Anything below will be less, and above will be more. It is a great way to determine the true USE of an engine.
These are sometimes also simply called analog hour meters.
The newer digital meters run as long as there is power going to the alternator. I don't think they give as accurate an idea of the wear of an engine as they measure every moment it's on rather than reflect the different RPM usages.
John
Most will say that rated speed is necessary to get one hour's use in one hour. Anything below will be less, and above will be more. It is a great way to determine the true USE of an engine.
These are sometimes also simply called analog hour meters.
The newer digital meters run as long as there is power going to the alternator. I don't think they give as accurate an idea of the wear of an engine as they measure every moment it's on rather than reflect the different RPM usages.
John