Penrose, R (2004). The Road to Reality: A Complete Guide to the Laws of the Universe. Vintage Books, გვ. 410–1. ISBN978-0-679-77631-4. „... the most accurate standard for the metre is conveniently defined so that there are exactly 299,792,458 of them to the distance travelled by light in a standard second, giving a value for the metre that very accurately matches the now inadequately precise standard metre rule in Paris.“