Awhile back, someone explained to me how to thread the machine when sewing with twin needles. I did thread my machine, but the underside (bobbin) thread didn't look right. I want to say the bottom stitch looks like a "zigzag" stitch, but the more I look at it, it looks like the tension needs adjusting (tightening, maybe?) I know it's not a good picture...I took it with my cell phone and had to do some editing. It's the best I could do. The picture below is the UNDERSIDE of the fabric with the stitch in question. Thank you.