While Mileage Is Typically An Effective Measurement Of Maintenance Intervals On An Engine Looking At The Actual Run Time Is The Best Way To Determine When Critical Services Need To Be Performed. Autometers Electronic Hour Meter Provides A Highly Accurate Measurement Of Your Engine Hours And Allows You To Make The Best Possible Decisions As To When A Service Needs To Be Performed For Maximum Service Life And Return On Investment. This Gauge Does Not Have Illumination.