If you want the easiest way, the digital thermometer hygrometers are the way to go, When I first started hatching, I thought that digital was the way to go, After trying several different brands of the cheap digital hygrometers, I learned that they are just not accurate enough for me.  I have 3 incubators, so I bought 3 digital thermometer/hygrometers and I would get different readings from all 3. And with the cheaper ones there is no way to calibrate them.  With my old fashioned dial thermometers, I can move them from incubator to incubator, and I get the same reading from all of them.