As of version 3.1, in:Flux can display a grid overlay in the 3D window. This option can be toggled on and off similar to the clip plane by clicking the () icon on the toolbar. If you are not currently in Orthographic mode, you will be prompted to do so. The perspective can be changed from the view menu or by pressing Ctrl+P on the keyboard.
Upon toggling the grid on, the Grid Options window will appear, shown below.
Various options are available to edit:
Visible - toggles the visibility of the grid overlay. This is synced to the button on the toolbar.
Anchor point - sets the starting coordinates of the grid overlay, rather tha the default origin. This could be set to a leak location for instance.
Type - linear and radial grid options are available
Color - sets the color of the grid lines and text
Font size - sets the size of text on the grid
Note, toggling the visibility off of the overlay from the toolbar will close the Grid Options window. Click the toggle button again to open the window back up.