HP 4 FAMILY - Manual (Page 94)

Vertical Clusters
Vertical clusters are groups of two or three narrow
characters side-by-side in a vertical line of text. Vertical
clusters containing half-width characters can be created
by using a combination of print direction and cursor
positioning commands.
An example of vertical clusters is shown below. The C
program that follows was used to generate the PCL
commands for this example. In this example, two half-
width characters (e.g. 2-digit numbers) were printed as
vertical clusters.
2-58 Printer-Specific Differences