William L. Shirer, The Rise and Fall of the Third Reich
http://www.onwar.com/chrono/1940/jul40/f31jul40.htm
British produce more fighters
Wednesday, July 31, 1940 www.onwar.com
In Britain... Fighter output for July is found to be 50 percent above the target figures. Since May 1st 1200 fighters have been produced. This is more than have been made in Germany and the RAF is therefore closing the numerical advantage of the Luftwaffe.