"Based on engine operating
conditions and accumulated engine
revolutions, the onboard computer in
your vehicle calculates the remaining
engine oil life." - Civic Owners Manual
With the emergence of fuel injection and consequently the Engine Control Unit as the standard method of "making it zoom", we have at our fingertips a heretofore untapped wealth of digital information that can be used to retire the mileage-based maintenance schedule along with those defunct carburetors. The raw data is available - drive-by-wire throttle inputs, engine temperature information, accumulated number of RPMs, even calendar time. (Shoot, instead of trying to hold it in your brain how long it's been, since your last oil change, why not let some computer do it?) And all of these inputs may be correlated to estimate how hard the car is being driven - patterns of hard acceleration, long periods of steady throttle, stop-and-go ... it's all there, being stored away in a memory chip. The car remembers how you drive. While it can't test its own oil any more than we can test our own blood, it gives us the best estimate yet of when the oil might be worn out. Honda's Maintenance Minder (not a very sexy name, but it is what it says) taps into this capability to simplify life. There are seven maintenance operations designated A, B, 1, 2, 3, 4, 5. When the computer has counted enough RPMS and enough time has gone by, one or another of these lights up on the dashboard to say "hey, I need an air filter and spark plugs" or "oil change".
So yay. We don't need a computer to tell us when to change the oil, right? Well, remember that oil-change time is a guesstimate anyway. People say that oils these days last between 5,000 and 7,500 miles. But unless you pay to have an oil analysis done after three or four oil changes to determine the correlation between mileage and oil life, you won't know and you'll probably change the oil more often (and spend more money) than necessary. And even then, your estimate is based on mileage, inherently less useful in determining oil life than RPMS. The same mileage driven hard will wear out the oil faster than an identical mileage driven gently, given daily operation. In fact, if one has to choose a single criterion to base maintenance on, an RPM based maintenance schedule is probably the most accurate, even more so than hour-based maintenance.
The one factor, of course, that RPM based maintenance doesn't consider is how loaded or unloaded those RPMS are. A lot of hilly driving will put more stress on the oil for the same RPM than driving on level ground. However, a temperature data line (greater engine temps on hills) ought to weed out some of that variable. And of course there is to consider how dirty the air intake is.
In the end, service intervals are all estimates and must be treated as guesses. The question is, how can the most accurate guess be achieved for people who aren't into pulling plugs to look at the soot deposits, or analyzing their oil? Honda's answer seems to be pretty well thought out.
(p.s. Also, the Civic averaged 32 mpg on its fifth tank of gas in ordinary stop and go driving. That ought to improve as it breaks in)