corn snakes originate from the southeastern USA where humidity can range from 20% to 100%. You'd be better off with a gauge that measured an actual percentage rather than something that just says "Dry."
If all else fails, just watch your local weather. Whatever the humidity is outside at any given moment, it will be within a few percentage points inside as well, unless you are using a humidifier / dehumidifier, which obviously you are not or you would not be worried about it.
Corn snakes get along well with daily humidity readings of about 30 to 50 percent. It can fluctuate up and down, no big deal. You might want to get a clean spray bottle and lightly spritz the cage when the snake is shedding. But outside of shedding, there's really not much to worry about. Your "Low humidity" today could just as easily turn into High humidity tomorrow with a passing thunderstorm. Don't over-think this or take unnecessary action, as creating a higher humidity can do more damage to the snake than a low reading can.
You can also set up a "Humid Hide" for the snake which is basically an enclosed hiding area with damp moss inside. But again, this is usually only needed during shedding.