and you checked the oil in the same location both times? with the car parked in the same direction? level can vastly effect the dipstick.
it is possible, that your oil filter o rings are in need of replacement, and you are rapidly draining oil back into the crankcase. loosen the screws on the oil filter canister, and open the lid, then check the oil level again... see if it jumps back up to the full mark.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!