Chart symbol:
In this increase a stitch is added by working under the back ridge (back “bump” or back “hump”) of the horizontal chain between the stitch just worked and the next one.
Insert your hook from front to back under the back ridge of the closing chain (you made in the return pass) before the next st:
Yarn over and pull up a loop:
Leave the loop on hook:
One stitch increased in the row:
