On the Openings tab you define the dimensions and coordinates of openings in a slab.
To define an opening, do the following.
- Enter dimensions of an opening in the table.
- Indicate the position of an opening in a slab in the table or graphically in the drawing.
The position of an opening is determined by the coordinates of the its bottom left corner.
Changes of coordinates in the table results in a change of slab geometry in the drawing.
The top right part of the dialog holds the following tools.
Toggles the ruler. 
Translates / changes the reference point (switching on / off). 
Defines the grid. Cells of the grid (in the direction X and Y) and a position in the coordinate system may be defined. - - Toggles the graphical definition of an opening.