The document is applicable to the calibration of photometric measurement procedures in the field of haemostaseology. The calibration can be carried out with the aid of serial dilutions of a defined normal plasma (aktivity = 100 % or 1 IU/ml) or of a calibration plasma or with the aid of several undiluted calibration plasmas with an exactly determined activity or concentration of the coagulant constituent to be analyzed (e.g. fibrinogen in g/l).