Describes the results of a study into the effect of a dedicated calibration facility on the calibration relationships for hot-wire probes. Calibrations were carried out with plated and unplated normal hot-wire probes using both parallel and perpendicular support orientation in a calibration facility with variable nozzle exit area and in a wind tunnel. The results obtained clearly demonstrate that the cross sectional area of the calibration flow has a major effect on the evaluated calibration relationship. In particular the results for the parallel support orientation show a continuous variation in the interpreted velocity with cross sectional area. The difference between the 12 mm² and the 120 mm² nozzles was about 3-4% and a further difference of about 3-4% was observed for the wind tunnel comparison.