in her song "diamonds and rust", singer/songwriter joan baez refers to "a voice [she'd] known a couple of lightyears ago". the use of lightyears as a unit of time implies that "diamonds and rust" does not internally use the si system of units, but rather a geometrised system of units. whether or not the speed of light is taken to equal 1 in the song, as is typical for geometrised systems of units, is unclear
