This "secret sauce" procedure was discovered in 2001, and it is in the long lost archive, now. So I thought it might be helpful to resurrect this one. It works for the 2001-2004 cars. There must be a similar procedure for the 2004-2007 W203s, so maybe someone will post that in addition.

This is how you electronically -- and accurately -- measure the oil level in the W203. This must be done on level ground with the motor absolutely COLD 2-hours or more. (ie, all the oil drained into the sump) Checking at the end of a refueling stop will NOT be accurate... The motor retains a lot of oil when warm or recently running)

1. To start, the key must be removed from the ignition.
2. Insert the key and turn to position 1.
3. Press the "Page Down" steering wheel button (lower Right button on the left side) to select any MFD display other than a trip odometer. (Don't do this and you will reset your trip odo).
4. Immediately press and HOLD the trip odometer reset button (left edge of instrument display) until the instrument cluster beeps. There is no visual message, only an audio beep. Turn down the audio system and be patient, this takes around 40 seconds. (Your trip odometer page may return in the MFD, but it will NOT reset to zero if you properly did step 3, so don't worry) After the beep...
5. Press the "Page Down" steering wheel button again.
6. The MFD will show the page x15jq has posted above, except the oil level values will be "dashes".
7. Turn key to position 2 and wait while system measures the oil.

You should turn the key off and remove it to reset the system before driving. But, you can actually turn the key to position 3 (start) instead, and drive with the screen up.

When I learned of this procedure in May 2001, I checked my C320, which at the time was only 2-months old and still had its factory fill of oil. The reading was 8.0 Quarts, exactly. Again, let the car cool off OVERNIGHT on level ground before starting this test.

Even though the manual says 8.5 qts, it won't hold more than 8.0 without giving you a Fault page saying "Oil Level too HIGH... Lower Oil Level." I learned this the hard way. After an "A" service at the dealer (under the maintenance included program), the level read 7.4 Qts. So I insisted the dealer top-off to 8.0 on a warm engine. A few days later, I started getting the "Too High" fault codes, so I remeasured it when cold one morning and it said 8.2 qts. I siphoned off some of the oil (through the dipstick tube) and it now reads 8.0... no more fault codes.

Just make sure your motor is dead cold when you measure your oil to ensure that you measure every drop accurately.