To buy this humidistat certainly come in handy this review ,but these days was detected a serious error about which you can read in the following lines.
The humidistat worked really well, it was enough to calibrate the correct humidity and have reliable device was accurate , but there is one hidden defect:
If you calibrate the humidity controller to a negative value such as -1, turn off the power suplly,humidity controller does not remember any value!!!!
Set value after blackout is 50% value for CAL is 0.
If you calibrate a positive value, for example, +1 humidity controller remembers all values and working correctly.
I tested 10 items from various suppliers from eBay and aliexpress and all 10 units had this bug. A possible solution is connected through a humidity controler with backup power. Is good humidity controller but this bug is realy serious.