The importance and necessity of a tachometer as an instrument of Service equipment cannot be stressed too emphatically - in reality it's the modest assistant that puts the final OK on a job of engine tune-up, repair or installation.

It tells you in the test room whether or not the engine (motor) with appropriate test wheel installed, is measuring up to the performance characteristics established for it - by counting the RPM under full throttle running conditions. Should it fall short, it's back to the bench for further diagnosis and corrective steps.

It tells you on boat installation whether or not the propeller selected is correct for the purpose - again by simply counting RPM at full throttle position for maximum performance. And again, should it fall short or over rev. it tells you which way to go on the propeller - down pitch or up, assuming the installation to be proper.