Salt-Test Calibration

Storage & Aging
Definition
A method of checking a hygrometer by sealing it with a slurry of table salt and distilled water, which produces a stable 75 percent RH environment at room temperature after several hours.
Why it matters
It is the only cheap way to know whether a hygrometer is telling the truth, and cheap units are often off by five points or more.
In context
"The salt test showed the gauge was reading four points high."