This applies to imageset and printed output. It has no connection with the computer’s monitor screen. Screen frequency is often called just 'screen'. Printers and printing machines reproduce tints of a basic ink color as small dots arranged in rows. Screen frequency is the spacing of these rows and is usually measured in lines per inch (lpi). A desktop laser printer often has a coarse screen of about 60 lpi and the individual dots are noticeable. Imageset output is normally 100 to 150 lpi and you need a magnifying glass to see the dots. For imageset output, your print shop can tell you the screen frequency to use.