The vacuum-calibration apparatus is mainly composed of the extreme high-vacuum (XHV) system, ultrahigh vacuum system, and separated-flow system. The ultimate pressure of 7.9 x 10(-10) was obtained in the XHV calibration chamber by combining the magnetically levitated turbomolecular pump and nonevaporable getter pump (NEGP). The separated-flow method was used to extend the lower limit of vacuum-gauge calibration to 10(-10) Pa. The uncertainty at lower limit was reduced when taking inert gases as test gases because NEGP has no pumping speed for inert gases. For this apparatus, the combined standard uncertainties were estimated to range from 1.5% at 10(-4) Pa to 3.5% at 10(-10) Pa. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3457934]