To calibrate a humidity sensor, switch the meter off by pressing POWER. Remove the black ball and dust filter, then insert the brown bottle screw. Long-press the POWER, BACKLIGHT, and PAGE buttons to enter calibration mode. The mode banner blinks and shows a value of roughly 32.0%, indicating that calibration is underway. After 60 minutes, the mode banner stops blinking, indicating that the calibration process is finished. Place the humidity sensor into the 75% NaCl salt solution after taking out the salt bottle. Press PAGE for two seconds to begin the high rh% calibration mode. The mode banner blinks and shows a value of roughly 75.0%, indicating that calibration is underway. Once the meter has been turned off, remove the salt bottle.