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

EN Drawing Arcs 20-7
Angle of Rotation
NoteS A positive angle of rotation is in the direction of the +X-axis to the
+Y-axis as shown below.
A negative angle of rotation is in the direction of the +X-axis to the
−Y-axis.
Figure 20-4 Drawing arcs (2 of 3)
Note The relationship of the +X-axis to +Y-axis (and -Y-axis) can change as
a result of the scaling point or scaling factor changes, thus, changing
the direction of a positive (or negative) angle of rotation.
You can also draw arcs using the Absolute Arc Three Point (AT) and
Relative Arc Three Point (RT) commands. These commands use
three known points (your current pen location plus two points you
specify) to calculate a circle and draw the appropriate arc segment
of its circumference. The arc is drawn with a positive angle of rotation,
so that it passes through the intermediate point before the end point.
Refer to the following illustration.