The present time is on the left of the graphs and the past is towards the right with the scale in hours.
- The blue line indicates the difference between the air and infrared sky temperature. Higher numbers generally mean clear skies, lower numbers mean clouds. Note that the sensor is quite "blind" to high thin clouds. When the sensor is wet, it is set to 0.
- The green line is the threshold used by the observatory to decide between clear and cloudy skies.
- The red line is the threshold used by the observatory to decide between cloudy and very cloudy skies.
- The black line indicates the sky brightness (the day/night cycle). When it is near 0, it is daytime.
The data originates from an AAG Cloudwatcher cloud detector.