Volumetric glassware is always calibrated such that the measured volume is specified by reading the calibration of the BOTTOM of the aqueous meniscus. So I make that volume in the illustration to be $20.01 \cdot m L$. (Do you agree? I think I need to put some reading spex on!).
The calibration on a burette is $\pm 0.1 \cdot m L$. Your eyes should be good enuff to read to $\pm 0.01 \cdot m L$.