Option Switch 1 only operates on plotters that use a plot roll rather than single sheets, and when OS 31 is set at 0 to obtain multiple isometrics in each plotfile such as that shown in the following illustration.
OS 1 is not effective if OS 31 is set to 1 so that each plotfile contains only a
single isometric. As a result, it is not used when single DXF or DGN plotfiles are
produced for importing into a 2D graphics system, such as AutoCAD or MicroStation,
where isometric drawings are usually sent to a laser printer for plotting.
Some older plotters, such as Benson Electrostatic, have a maximum plotfile length of 3275mm, which is the default setting for OS 1. Other similar plotters use a different maximum length value. Under these settings, the software considers the physical drawing size and stacking arrangement and will output the maximum number of isometrics it can into each plotfile produced. For example, if 20 isometrics are produced, you can get three plotfiles--two containing three isometric drawings each and one containing four isometric drawings.