I use a kids composition book ... date, mileage, event, symptom/resolution if applicable. It comes in very handy to see how much oil being used, mileage in a year, "did I replace the spark plugs before or after John Entwhistle died" (though I discovered the car had not been made until after he passed so I consider which presidential administration was in charge at the time).

__________________
2003 X5 3.0 - Original Owner