1. http://www.lauda.ch/Download/Was%20ist%20analog%20und%20digital.pdf.
2. Analogrechner
3. a)http://www.calculino.com/de/schule/abakus‐rechenschieber_information.html. b)mathe‐abakus.fraedrich.de/abakus/abakus.htmlc)https://www.ee.ryerson.ca/~elf/abacus/roman‐hand‐abacus.html. d)https://en.wikipedia.org/wiki/Roman_abacus.