MACROMEDIA FREEHAND 10-USING FREEHAND Use Manual page 399

In addition, because different types of paper absorb inks in different ways,
the characteristics of your paper and the press also determine the screen ruling
you should use.
When setting the screen ruling for grayscale images, the maximum number of
grays possible in an image is 256. Increasing the screen ruling decreases the
number of grays available. The maximum number of grays that can be used in
Gradient fills or blends depends on the capability of your final output device and
the maximum steps value.
For color images, follow the guidelines in the table for specifying a screen ruling:
For grayscale images, follow the guidelines in the following table:
If you've included screened objects in your artwork, you can select halftone
settings for selected objects, to print those objects at halftone settings that differ
from those applied to the document as a whole.
You can override object-level halftone settings when choosing Separations options
in the Print Setup dialog box. For more information, see "Setting separations
options" on page 396.