In this paper we revisit the Adler-Bobenko-Suris H2 equation. The H2 equation is linearly related to the S (0,0) and S (1,0) variables in the Cauchy matrix scheme. We elaborate the coupled quad-system of S (0,0) and S (1,0) in terms of their 3-dimensional consistency, Lax pair, bilinear form and continuum limits. It is shown that S (1,0) itself satisfies a 9-point lattice equation and in continuum limit S (1,0) is related to the eigenfunction in the Lax pair of the Korteweg-de Vries equation.