Történelmi áttekintő

[Ábrák:

http://www.actiweb.es/mathclass/pagina5.html

http://www.mandm.org.nz/wp-content/uploads/2012/12/scales.jpg

http://www.rumvi.com/products/ebook/%D0%B2-%D0%BF%D0%BE%D0%B3%D0%BE%D0%BD%D0%B5-%D0%B7%D0%B0-]

[Ábra: http://www.atom.rmutphysics.com/charud/oldnews/0/286/15/1/ATLANTIS/Albert_Einstein.jpg]