System One Humidity Control has been designed to establish optimum patient comfort and device performance. For additional comfort, System One now has improved absolute humidity and target relative humidity levels across all humidifier dial settings. In addition, a new “classic” mode provides the ability to shut off humidity control. Even in changing environmental conditions, consistent humidification levels are preserved throughout each night. System One closely monitors room temperature, room humidity, and flow to determine what is required to maintain the patient-selected humidity level. By controlling relative humidity output at the mask, rainout can be prevented, under most circumstances. Through a combination of our cleverly-designed water chamber plus the advanced Dry Box design, the risk of water ingress into the device is virtually eliminated. Even when fully filled, to the fill line, the water chamber can be tilted or turned upside-down without leaking back into the device. Should any water manage to escape the chamber, the Dry Box prevents it from entering the device.