# Variables from Doors and Windows

In doors and windows the first combined element primarily determines the properties and the construction. Therefore its variables are passed on to the subsequent combined elements. These variables are now also forwarded to the HRB assignment when they have been defined there as external variables.

In the opening settings or in the intermediate values in HRB the variables are used in the formulas. During the assignment the HRB interpreter takes the values for that specific opening at each opening. This enables very precise control of each individual window. This is suitable, for example, for transferring information about belt drives or the type of lower connection for floor-to-ceiling windows (balcony, terrace, façade).

Special possibilities arise here when using IFC Premium: via the mappings the variables of the first combined element can be addressed directly. A specific value, for example "air at bottom", can thus be controlled via IFC, so that the requirement from the production planning can be transferred all the way into the HRB assignment.
