Book excerpt: In order to improve icing cloud uniformity, changes were made to the tunnel at the NASA Glenn Research Center in the vicinity of the spray bars. These changes necessitated a complete recalibration of the icing clouds. This report describes the methods used in the recalibration, including the procedure used to optimize the uniformity of the icing cloud and the use of a standard icing blade technique for measurement of liquid water content. The instruments and methods used to perform the droplet size calibration are also described. The liquid water content/droplet size operating envelopes of the icing tunnel are shown for a range of airspeeds and compared to the FAA icing certification criteria.