Thanks to all of you for your advice. All comes to those who wait, but
patience is not one of my virtues. It took about a minute the first time, but
after I had restarted the computer and tried again the charts appeared more or
less instantly. This is on bog-standard AOL dial-up. Maybe my computer
requires a spring-clean.
As to the charts themselves, the pressure anomaly must be close to a
record for a summer month. It's certainly the lowest mean August pressure I
have recorded in 21 yrs, though 1992 and 1999 come close. I would imagine the
anomaly distribution for August 1968 would also be a sight to behold.

Tudor Hughes, Warlingham, Surrey.