The splitting program permits division of an existing grid into two separate grids. It is used most frequently to remove surplus parts of a grid outside the open boundaries, after the latter have been positioned. It can also be used to split a large grid into smaller parts, either temporarily, to facilitate editing, or permanently, to provide grids for smaller models. (The opposite process of joining together small grids to make a larger one can be carried out by means of the Editor). The Splitter displays the existing grid and prompts the user to design a closed "splitting" polygon. The parts of the grid inside and outside this polygon are arranged by the program into two separate self-consistently numbered grids. Before splitting can be carried out, the user must select suitable vertices near the polygon and move them to the nearest side of the polygon, otherwise non-triangular elements will be created when splitting occurs. As well as facilitating movement of vertices, the program also reminds the user to enter appropriate computing codes for each vertex moved to the new boundaries formed on splitting.