The Protimeter Calibration Salt With Adapter BLD4790, BLD4790-AD allows users to accurately check and calibrate the humidity probe at a fixed 75% Relative Humidity (RH). This calibration set ensures that your Protimeter instruments maintain precision in humidity readings, which is critical for reliable environmental and moisture analysis. The kit includes a Calibration Test Bottle (BLD4790) and an Adapter (BLD4790-AD), which are sold separately to meet your specific calibration needs.