↑ Nelson, Robert A. (1981), "«Foundations of the international system of units (SI)»", Phys. Teacher: 596–613, <http://plato.if.usp.br/1-2009/fmt0159n/PDFFiles/ThePhysTeacher_FoundationsOfTheSI.pdf> Архивная копия от 6 июль 2011 на Wayback Machine.