Seiko Instruments SII Black-and-White Raster Plotter LP-1020 - Manual (Page 144)

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■PLAN SIZE (HP-GL only)
Sets which command is to be enabled as a drawing size command. Sets
data to OFF if the drawing size is not properly set. This setting is
performed on the third hierarchy.
: Default value
ON (PS) Sets the PS command as the drawing size.
ON (IP) Sets the IP command as the drawing size.
ON (IW) Sets the IW command as the drawing size.
OFF Disables the drawing size command.
You need to set ON (IP) and ON (IW) only when it is clear that the IP
command or IW command is used as the drawing size, to avoid causing a
printing error. (It depends on the CAD application.)
If the PS command is available when setting ON (IP) or ON (IW), the PS
command is given priority.