ScreenGrid

Creates a custom-sized grid on your screen made of black lines. The grid will cover the entire screen, allowing any movable UI elements to be arranged and aligned. Moving UI elements may require an additional, non-included addon.

Usage:
/screengrid x - x should be the number of lines to be displayed. To hide completely, use /screengrid 0 or /screengrid.
/sg can be used as well

Note:
At a low number of lines (less than 16 or so), boxes may be cut off due to individual screen resolution. At a high number of lines (256+), the screen will start to become unreadable. I suggest 32-64 for larger elements, and up to 128 for fine-tuning.