This parameter can be used to speed up the rendering process. The default value is 0.
If set to a number then only some Vertical pixels will be generated. e.g. if set to 1 then only every other line will be generated. The others will be copied from the previous line. This can be overridden by using ARexx. Also see DX.
It can be changed using the menu item (if reqtools.library is available), a requester is displayed allowing the input of the value.