QMS 2425 Reference page 129

frequency determines the number of halftone dots used to represent
gray levels in a given area.
The following formula shows the relationship between screen fre-
quency, print resolution and gray levels. As the screen frequency
increases, the number of gray levels decrease. If resolution is
increased, the number of gray levels will also increase.
2
gray levels = (resolution/screen frequency) + 1
You can change screen frequency by selecting the halftone type in
the QMS 2425/2425 TURBO configuration menu (see the table in
"Halftone Types" on page 5-6), through your application, or by using
the PostScript setscreen operator.
The extra gray levels available through a higher resolution provide a
smoother shift from the darkest black to very light grays.
A screen angle is the angle at which a halftone screen prints. The
default screen angle for your QMS 2425/2425 TURBO Print System is
45° at 300x300, 600x600,and 1200x1200 dpi. This is the normal
angle for black and white printers. The Advanced halftone type option
varies the screen angle (see the table in "Halftone Types" on page 5-
6). You can also change the screen angle through the PostScript set-
screen operator.