Epson 4500 - Manual (Page 123)

Graphics
The illustration below shows how you can use a grid on paper to plan
where you want dots to be printed. This grid is for a single line of
graphics 42 columns long. Since each line of 24-pin graphics is
approximately 1/8th of an inch high and since triple-density graphics
prints 180 dots per inch horizontally, a design planned on this grid will
be about 1/8th of an inch high and less than 1/8th of an inch wide.
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The actual pattern that the printer prints on the paper is, of course,
made up of dots that overlap each other both vertically and
horizontally. The reason the planning grid uses an x for each dot is that
using an accurate representation of the dots makes calculating the data
numbers difficult because they cover each other. Therefore, remember
that each x represents the center of a dot, and the dots actually overlap.
Write the assigned values of the pins next to your design, then total the
values for each column of dots. These totals are the values that you
send to the printer as graphics data to print the design.
4-16 Software and Graphics