Pfaff fashion Owner's Manual page 28

Sewing
3:5
Formation of the stitches
The stitch formation varies.
Some patterns are formed from the left, so only the
right side of the stitch changes when the width is
adjusted. The left-hand side of the stitch is always
retained.
The patterns that are formed from the right will always
retain the right side of the stitch, regardless of any
changes in width.
Note: Do not use a twin needle to sew patterns that are
formed from one side! Do not use a twin needle if this
symbol in the window lights up.
Patterns that are formed from the center will change
equally from the right and the left when the width is
adjusted.