Take the Preview Dialog of the ZWCAD as the example, here is the introduction of the setting of the CAD blocks preview.
The list of options:
Frame to preview: Specify the displaying position of the drawing presented in the preview area which you select by left-clicking.
Global Scale: Preview the whole drawing
Zoom in: Zoom in the drawing in the preview area.
Zoom out: Zoom out the drawing in the preview area.
Maximize: Maximize the "preview" dialog box.
Recover: Recover the "preview" dialog box.
Full: Full screen.