The herpstat has 3 humidity regulating modes:
1. is based on the system clock (basically a big timer)
2. used the herpstat humidity probe (a digital hygrometer probe) to measure humidity then use that data to turn the misting system/humidifier on/off
3.is a hybrid of the first 2.
More info here: http://spyderrobotics.com/products/h...t12_manual.pdf (page 4)