Continue measurement (subtract) 
Using this button, you can continue the selected measurement in cases where you wish to subtract the area of already drawn surfaces (e.g. in the facade, by removing the surface area of the wall openings). By doing so a new sub measurement is created (See Drawings/Continue measurement). The surfaces that you remove from the measurement are marked on the drawing with cross-hatching, while the outline of the areas removed is marked with a dashed line. In length measurements you can also remove parts of lines which are then marked with a dashed line.
Continue
measurement (subtract) cannot be performed on count measurements 
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