The MODULEF software package consists of a set successive layers (figure ).
In the same manner in which Fortran is a higher level language than machine language, MODULEF consists of four layers which are situated on top of that of Fortran. The layers situated at the highest levels are the easiest to employ, however, for certain problems it is necessary to return to the layers at the lower levels.
Figure: Utilisation Levels.
In this manner, the user can place him/herself in any of the following situations, listed in the order of increasing difficulty (from highest to lowest levels):
These four situations are described below.