Select Add Field
Point Grid 
from the toolbar or the Grid
menu.
You will see the Grid Properties dialog.
A Field Point Grid can be manually defined at any location with the Add Field Point Grid option. To manually add a Field Point Grid:
Select Add Field
Point Grid from the toolbar or the Grid
menu.
You will see the Grid Properties dialog.
For a manually added grid, you can specify the Number of Grid Points.
The grid expansion factor option is disabled, because this is only applicable for the Auto Field Point Grid option.
Enter the number of grid points and select OK.
NOTE: if a grid was previously defined, it will be automatically deleted when you select OK.
You will now be prompted to enter two points which define opposite corners of the grid. You can enter the two points graphically with the mouse in the Plan View, or you can enter the x,y coordinates of the two points in the prompt line.
After the second point has been entered, the grid will be added to the model, and the analysis will be automatically computed. The computation may take a few seconds or more, depending on the number of grid points, and the complexity of your model.
Grid Properties
After adding a grid, you can change the Grid Properties (i.e. number of grid points) with the Grid Properties option. This allows you to change the number of grid points, without having to re-enter the coordinates of the grid.