Cadillac Repair: Oil % reading, cadillac deville, oil life

Question
I just had my oil changed because the oil % reading was at 20%, after the oil was changed its at 18%. Can someone explain this to me. I have a 1998 Cadillac Deville Concours

Answer
To reset the engine life monitor:

1. Turn ignition key ON. Do NOT start the engine.

2. Keep pressing and releasing the TRIP button on the drivers information center until you see OIL LIFE REMAINING.

3. Press and HOLD the RESET button on the drivers information center and HOLD it IN until the display reads 100% and then release the button.

4. Turn ignition OFF.