Singer 14T967DC Workbook page 96

Fold sweatshirt fabric wrong sides together,
lengthwise.
Align the fabric so that the fabric's fold is not
being trimmed by the knife.
Sew.
Gently pull the fabric flat and press.
Hint:
If the fabric is not laying flat, align
the fabric farther to the left of the
knife.
Three-Thread Flatlock (wide) page 6