System One Humidity Control for Comfort Delivering consistent humidity levels throughout the night, at the mask, improves sleep therapy comfort and compliance. The System One uses a simple dial to adjust relative humidity at the mask. What The PR System One's Humidity Control system monitors room temperature, room humidity, and air flow enabling it to maintain your preferred humidity levels, even when environmental conditions change. By controlling relative humidity output at the mask, rather than simply setting the humidifier temperature at higher or lower levels, System One Humidity Control provides a custom sleep experience and it helps prevent rainout too!