A general plan of the mountain is shown in Figure 1.3. Figure 1.4 shows the fraction of usable time for each month, averaged over the past 15 years. Figure 1.6 shows a histogram of the seeing measurements recorded by AAT night assistants at the start, middle and end of each night over the five years 1984-1988. There is, however, a significant deterioration in seeing over the course of a typical night. This may be associated with a trend for the seeing to worsen when the air in the dome is colder than the mirror, which usually happens later in the night as the air temperature drops.
Further tests are in progress.