CDI Oil Level Measurement Inconsistency

[shertex]

As you CDI owners may know, you can measure the oil level not merely the way the manual tells you to (reading OK, or add a quart, etc.), but you can get a reading that is precise to the tenth of a quart. But as I've done it recently (trying to figure out if I'm using any oil), I've gotten inconsistent measurements, ranging from 6.7 quarts to 6.9 quarts, or a 6 oz. range. Measurement is always taken at the same spot on the driveway, always after the car has been brought up to operating temperature, and always after plenty of time has been allowed for oil to drip into the pan.

I don't understand how, after sitting overnight, it can read 6.7 but then, after sitting for only two hours, it can read 6.9.

Am I overlooking some variables? Or is the system just not all that accurate?