More precisely, it is defined<ref>[http://mathworld.wolfram.com/Curl.html Curl] at Wolfram Mathworld</ref> as the limiting value of rotation per unit area. Written explicitly, | More precisely, it is defined<ref>[http://mathworld.wolfram.com/Curl.html Curl] at Wolfram Mathworld</ref> as the limiting value of rotation per unit area. Written explicitly, |