HP PCL/PJL reference (PCL 5 Printer Language) - Technical Reference Manual Part II

EN SI, Absolute Character Size 23-77
A negative height parameter mirrors labels in the top-to-bottom
direction.
SI.6,-.9;LBPrint#;
Figure 23-36
Negative width and height parameters together mirror labels in both
directions, causing the label to appear to be rotated 180 degrees.
SI-.6,-.9;LBPrint#;
Figure 23-37
Table 23-47
Related Commands Group
AD, Alternate Font Definition The Character Group
CP, Character Plot
DI, Absolute Direction
DR, Relative Direction
LB, Label
SB, Scalable or Bitmap Fonts
SD, Standard Font Definition
SR, Relative Character Size