Calibration laboratories are generally responsible for calibrations of industrial instrumentation. These calibrations require compensation to preserve consistent measurements. Differential photometry is the simplest of the calibrations and most useful for time series observations. Absolute numbers vary between pets, and with meter calibrations. Unlike earlier monitors, it operates without periodic blood-requiring calibrations. The intervals between calibrations depends on the environment where the surface plate is located. Psychometricians experienced with IRT calibrations and CAT simulation research are necessary to provide validity documentation. Other changes included an increase in specification, minor suspension calibrations, and refreshed interior trims. Six-place balances and environmental controls dramatically increase the cost of such calibrations. Over the outer-Elbe-estuary in the Wadden Sea further calibrations and tests were made. The equipment is also portable allowing calibrations to be done when and where required. The large sample sizes (typically hundreds of examinees) required by IRT calibrations must be present. In 1990, a fixed conventional value was defined for use in resistance calibrations worldwide. For high-frequency calibrations a Dicke switch is used here. Calibrations for AVHRR channels 1 and 2&colon; review and path towards consensus.