Information was obtained from the address http://davidpratt.info/cropcirc1.htm, and the following, loosely translated and supplemented by information obtained through search engines.
Taarifa zilizopatikana kutoka alikuwa http://davidpratt.info/cropcirc1.htm anwani, na Ifwatayo, kutafsriwa na kuongezewa habari zilizopatikana kwa njia ya injini ya utafutaji.