Brother HL-Series Technical Reference Manual page 12

User units
Vector graphics
Vertical plot size
VMI
you switch on the printer in LaserJet mode or change to LaserJet emulation
from another emulation mode. You can reset the printer to its user default
settings either by using a printer command or using the control panel.
Coordinate units specified by the user with the HP-GL and HP-GL/2 SC
command.
A method of defining graphic images in terms of coordinates, points and
lines. The HP-GL and HP-GL/2 graphics language uses this method.
The original vertical size of an imported HP-GL and HP-GL/2 image.
Vertical motion index. The vertical distance that the print position moves
down the page when a line feed is performed. This can be set using printer
commands or with the printer's control panel by adjusting the "Lines" menu
option in PAGE FORMAT MODE.