The internal vacuum sensor is a thermal conductivity Convectron(R) model 275 vacuum gauge. It can be calibrated in-place by comparison to a higher performing vacuum sensor such as a capacitance diaphragm gauge ("CDG"). The attached procedure is an excerpt for the PG7601-AF user manual. Accessory hardware is required for connecting the CDG to the PG7601 and these kits are detailed at the start of the document.