Hi, I don't have the manual for my Dressmaker Sewing machine and haven't used it in so long I'm having trouble remembering the basics like:

What causes loose underside stitches and how do I fix it?
Thanks,
G.

It could be misthreaded or the tension not adjusted properly.

The tension is adjusted with the knob usually on the front of singers. It's not the stitch length, fwd/rev control or foot height. It's just before where the thread gets pulled from.