Dual stage means that the Itc-308 can control both a heating and cooling device. Alternatively, it can control a heating or a cooling device. This controller displays in Fahrenheit and Centigrade. Dual Display shows both measured and set temperature.
Use to control fermentation or kegerator temperatures. I have a similar (although not identical) controller from Inkbird. The base unit is the same (ITC-308), the temperature sensors are different. Check out my [Hands on Review] of that unit.
Inkbird Aquarium Dual Stage Temperature Controller + NTC Sensor, AC 100V – AC 240V. (ITC-308S + 1.97″ NTC Probe)
Also: Yeast Starters & Fermentation | Kegerator Tips & Gear | ITC-308 Review | Homebrew Temp Controller Roundup! – Kegerator and Fermentation – concepts, applications and models