OK,
have a look at the attached. I removed ALL merged cells. I made the notes column wider and set the format to auto-adjust the row height. This results in a more consistent data table.
The mileage today is estimated in cell H2. Cells I2 and J2 show the mileages for the next oil change and tire rotation. When the estimated current mileage is within 1000 miles of these values, the respective cells will turn red, if the estimated current mileage is within 500 miles of these values, the respective cells will turn red.
You can enter new data at the bottom of the table any time. The three cells I added to the sheet will adjust their readings to the last data item entered.
Does that do what you need?
cheers, teylyn