I found this increase in a pattern for a garter stitch shawl a few years ago. It was used for the centre increases as it was a solid shawl with no lace. It is similar to a m1 but is worked over 2 rows. I find it sits better than a m1.
To work the increase in stocking stitch: yo where you want the increase, in the next row purl tbl when you get to the yo.
To work in garter stitch: yo where you want the increase, in the next row knit tbl when you get to the yo.