Epistemologically, hisab (calculation) and rukyah (sight) are different subject. Each of them has its own method, the basic, standard and validity of knowledge, so that the decisions they make are also different. Hisab is based on normative postulates and mathematics, while rukyah is based on normative postulates and empirical knowledge. Therefore, both can be said right in accordance with their own epistemological basics, methods and the standards of validity.