Every race bike needs regular maintenance and an engine hour meter is just the thing to keep track of the hours your bike's engine has done.
I fitted a DRD hour meter to my RMZ450 straight after the engine was run in so I now know accurately exactly how many hours the bike has done. I mainly needed to know when to do my oil and filter changes but it's also handy for other regular maintenance jobs like adjusting the cam chain tension and checking valve clearances.
I fitted a basic model DRD engine hour meter, installation was pretty straight forward, you mount the meter itself somewhere easily seen but out of the way on the bike and then you have to wind a small diameter wire around your spark plug lead and into a recessed niche in the back of the meter (click the pic to enlarge).
When the engine is running the electrical pulses through the ignition lead induce a small charge through the wire which in turns powers the hour meter. The meter shows that the engine is running with a tiny little hourglass graphic in the display window and when you shut the engine off it shows the total accumulated hours.
There are various models of hour meter available, some have extra functions like having preprogrammed time intervals and the meter will alarm to let you know that the time has elapsed and so forth, some will also tell you your engines maximum rpm.
Mine is the most basic one, it just tells you how many hours that the engine has been running, that's all I need to know. I have a whiteboard on the wall of my workshop and whenever I perform some maintenance I write on the board the time when the task is next due.
DRD also sell a bracket that is designed to replace the washer under your headstem and the hour meter can mount on that. I cable tied mine to the frame rail under the tank shroud so it sits in the gap in the shroud. It's easy to see and it's out of the way.
I haven't had a problem with my DRD engine hour meter, they're a sealed unit so they're pretty well impervious to dirt and moisture and basically once it's installed you don't need to worry about it again.