When
sewing on terry or any fabric with loops and nap, generally a topping stabilizer
is used. These can be helpful, but have a limitation: They do not hold down the
nap past the actual stitch, which means outlines can be lost in the surrounding
fabric. Using the menu Utility->Add Knockdown Stitches you can create a
global underlay for the entire design. The underlay extends a few millimeters
past the edge of the design, which helps the overall effect.
These options are included for fabrics that react in unanticipated ways, and the only way to know what to adjust is through the process of test-sewing.
Knockdown normally stitches one direction, on a bias, but some users have asked for it to stitch both ways for additional flattening. This is what the Bi-Directional box is for. Alternately, the density can be increased to hold down in a tighter pattern.
Stitch length is adjustable if it helps with the nap. It is fairly universal at 4mm but some digitizers like to have control of it for other purposes.
Inflation controls the size of the knockdown. For its intended purpose, the Knockdown has to be larger than the design, but normally not a lot. Some may want to extend the size by increasing the inflation, which makes the embossed look of it stand out further.