Following a shutdown of the Stanley ionosonde between the 5th and 13th of April for essential antenna repairs, the instrument did not reboot correctly and ran from the 13th to the 17th April without making any ionospheric soundings.
Unfortunately the autoscaling software still made attempts to scale during this period, producing spurious autoscaled data. As these values had no physical meaning, the UKSSDC has since expunged them from our database.
The UKSSDC recommends that users delete any Stanley ionosonde data that they have downloaded for the period 18:00:00 13th April 2012 to 11:30:01 17th April 2012.
The Stanley ionosonde has since been replaced with a stand by machine, and seems to be running normally since about 13:00:00 on 18th April.
Stanley ionosonde data is available at http://www.ukssdc.ac.uk/cgi-bin/digisondes/cost_database.pl.