Calibration with the master-scale procedure provides a defined unit of measurement for direct comparison between subjective reports from different individuals, obtained at different occasions, and in different contextual settings. A standard set of reference stimuli and the environmental target stimulus are rated on the same scale. The applicability of this procedure was demonstrated by applying it to odor annoyance from environmental pollution at three sites in communities with steel industry (Study 1) and bio-fuel processing (Study 2). Series of pyridine concentrations were used as reference stimuli that, together with the environmental target stimuli, were judged with magnitude estimation by participants with normal olfactory function. The results provide annoyance estimates for each of the six sites expressed in master-scale units and in pyridine equivalents that are directly comparable with each other and with those from other environmental studies using this procedure.