I work in the graphic arts industry. When we still used film, the only way to calibrate was using the supplied transmission calibration card. We calibrated it every morning, then output a step wedge from the filmsetter to calibrate it for the day. You should be able to buy the calibration plaque from X-rite, but yes, they are expensive. Depending on how old it is, and how long since its last service, you may want to send it off to X-Rite for a proper calibration and service. We do that every year with our densitometers and spectrophotometers. Again, very expensive.