1. Bogue, R.W.: ‘Environmental measurement and instrumentation’, Finkelstein, L., Grattan, K.T.V., Concise encyclopedia of measurement and instrumentation, (Pergamon Press Oxford 1994), p. 90–95
2. Rumelhart, D.E., and McClelland, J.L.: ‘Parallel distributed processing’, Volume 1: Foundation, Chapter 8: Forming internal representations by error propagation, (MIT Press Boston USA 1992)