Strongarm Walking Foot Sewing machine User Manual page 12

The goal of setting tension is to have the knot made by each stitch lie in the middle of
the fabric and be no more visible on one side of the fabric than the other.
Tension can be set on the tension dial, as well as on a small screw on the bobbin. It
is rare to need to adjust the bobbin tension. In general you'll only need to adjust it if
you are sewing very fine fabrics with fine thread and small needles.