There is one point plotted every half hour on each graph. Most of the values plotted are instantaneous, with the following exceptions:

• Wind speed: average and maximum over the previous half hour, based on a sample every three seconds.
• Wind direction: direction most often observed over the previous half hour, based on a sample every three seconds.
• Sunshine: percentage of the previous half hour which was judged "sunny" by a binary sensor which classes each 36-second interval as sunny or not sunny.
• Rainfall: average rate over the previous half hour.

Note that there are some inaccuracies in the historical humidity and dewpoint readings before October 1998, in the rainfall readings for July and August 2001 and from time to time throughout 2005, and in several readings in July 2006.