# System Variables - Openings

In HRB, system variables have been accessible in openings since version 18.01. The following offer particular capabilities:

**ORK** Recess construction. Distance of the window frame from the front face of the wall.

**ONT** Depth of the niche measured from the opening side

**OB** Width of the shell opening as specified in the opening input.

**OH** Height of the shell opening as specified in the opening input.

**OIdnr** Identification number of the window / the door

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The other system variables are listed in the HRB editor under the Insert → Formula Editor in the group *Opening dimensions* listed.
