Viking Turissa Operating & Service Manual page 22

Fold the fabric as shown in the sketch. Both the
length and the width of the stitches may have to
be changed; it depends upon the fabric you are
sewing.
In the far left illustration can be seen how the
stitches fail to reach the fold line of the fabric,
indicating you should increase the stitch width.
In the middle illustration the stitch width has
been increased too much, leading to excessive
"bite", indicating you should decrease the
stitch width.
In the right illustration is shown how a correctly
sewn blindstitched hem should look. The seam
catches only one or two threads of the fold
line.