Grid 

The seventh group of preferences contains grid options (see Grid).

This 'working grid' is an auxiliary grid on the xy plane that allows the user to select the coordinates of points in its grid nodes, setting the 'Activate snap' option.
Also this grid is a visual aid to know the dimensions of the model.
Note: If the model has defined with cartesian mesh type, then this 'cartesian grid' is drawn instead the 'working grid'.
The cartesian grid define the tick location on the three axes: x y z, not only the x y as the 'working grid', and these location could be non uniform (not equi-spaced spans)

General options
Show axis: If this option is set, 2D axes are shown in the grid (X and Y).
Show grid lines: If this option is set, grid lines are shown. It's possible to show/hide grid with the grid button that is located on the bottom right part of the main window.
Show labels: If this option is set, labels of the major lines are showed.
Activate snap: If this option is set, snap is activated.

Center
X/Y Center: These options determine the position of the center of the grid.

Extents
X/Y Extents: These options determine the extension of the grid in the X and Y directions.

Spacing
X/Y Spacing: These options determine the spacing between grid lines in the X and Y directions.
Major line every: This option specifies the number of lines between principal lines in the grid.