Gross error detection has great importance and is the necessary step in process data reconciliation.Many methods have been published to solve this problem

but no one can guarantee consistently finding all of gross errors.A combinatory method based upon measurement test (MT) and nodal test (NT) is developed for practical use. The MT-NT combinatory approach makes use of both MT and NT tests and avoids any artificial manipulation.It also eliminates the huge combinatorial problem that is created in the combinatory method based upon nodal test or in the serial elimination method in the case of more than one gross errors in a large process system.