Accuracy of Dry Block Calibrator

Am not clear on the term accuracy usage w.r.t a dry block calibrator. We normally use 650 deg. C dry block calibrator and some people keep asking for 1 deg. C or better accuracy. Is it correct to use the accuracy term for this method of calibration, as I always wonder how that the accuracy which is claimed by any manufacturer is true. For instance it can be of controller used on it and it's response time. And how to compensate for Temperature drop to the ambient atmosphere.