When it says the side length of a cube was measured to be 20mm to the nearest millimeter. In this case, can I regard the maximum error for the side to be 0.5 mm? to compute the absolute error of the volume (if it was measured to be $8000mm^3$)? I am just confused with 'the nearest millimeter' how I should interpret this mathematically.
Thank you
Yes, the error of $\pm 0.5$mm would be assumed by "to the nearest millimeter". That means the unknown side length $a$ is bounded by $19.5$mm $ \le a \le 20.5$mm.