This chapter details the time and space discretizations used for writing the finite difference counterpart of the continuous prognostic equations in Chapter 4. After these preliminaries, the finite difference equations are given for the simplest case of options consthmix and constvmix. Note that throughout all equations were appropriate, numerical indices are exposed within expressions so as to match exactly with those used in the fortran code. This extra bit of detail is insisted upon as another way of insuring that complex formulations are correct. MOM uses a wide variety of options to configure variants of the prognostic equations in Chapter 4. The available options are explained in Part XIV and the steps for solving these equations are covered in Chapter 22.