Today, a quick little introduction to some commonly used Double Decreases. In non-lace knitting, you won't see them too often, usually you will see their Single Decrease cousins, k2tog and ssk. But in lace and open work, you see them quite often, usually at the center point or intersection of a pattern repeat.
From left to right (if you can see in this grainy photo), a Central Double Decrease, a Left Leaning Double Decrease, and a Right Leaning Double Decrease. Each one of these decreases 2 stitches. In the photo, they have a yarn over either side to balance the stitch count.
Central Double Decrease: Abbreviated as sl2-k1-p2sso. Slip 2 stitches as if to knit 2 together, knit 1 stitch. Then with the left needle, pick up the slipped stitches and pass them over the knit stitch and off the right needle. The Central Double Decrease is a key part of the pattern stitch in Sweet Oak Cardigan, where it pulls the stitches gently away from twin yarn overs into a subtle vertical ridge.
Left Leaning Double Decrease: Abbreviated as sl1-k2tog-psso. Slip 1 stitch knitwise, then knit 2 stitches together. Then with the left needle, pick up the slipped stitch and pass it over the k2tog stitch and off the right needle. Both Left and Right Leaning are used, for example, in Galiano Vest.Left Leaning variation: Abbreviated as k3tog-tbl. Knit 3 together through back of stitches. Personally, I don't find this as nice-looking, but it is an easy-to-remember mirror of k3tog. I think to get it nicer looking, you would have to switch the direction of the stitches by slipping 3 stitches, one at a time, as if to knit, then knitting them together, so a SSSK.
Right Leaning Double Decrease: Abbreviated as k3tog. Knit 3 stitches together.