The issue of a working hours meter as a sales plus is well-covered above. I replaced my Yanmar hours meter with a (mechanical) one, in order to keep my own log accurate, and know where I was in the life of various parts of the system (e.g., impeller, mix elbow). In order to roll the hours meter up to the estimated engine use (the sailboat was purchased new), I hooked the meter up to a 12v power source and left it there for multiple weeks until I got to the figure I wanted. Then I installed it.