near the knob should have 2 light indicator for red(above) and green(below).
check by opening the drybox for a while and close it again. See if your hygrometer registers the drop of humidity(testing if the device works).
ps. sorry this is only for older model, as pointed by ryechua
do you happen to get from amk hub too? mine is quite a new batch,no light.
Only when it reach "certain" point then will have green light for awhile,otherwise is no light.
i have problem reading where the point is,so i just shine a torchlight in.