Go to Office Depot and get those little one inch diameter round stick on
tabs. You see them as price tags at garage sales. Write the date and
tach time for the next oil change. That way you can simply compare the
tach time to the time on the tag. Tag comes right off when you want to
replace it with a new one.

http://www.dealersupplyonline.com/ and click on Lube Stickers.
$29.95 gets you a life time supply of date/mileage (ok, use hours here)/
Oil Grade static cling stickers.