Virginia's Charivari Shrug - One Side Done

I finished up the white stripe on the first side, so the shrug is basically half done.  I have figured out an easy set of modifications to enable folks to utilize as much of their yarn as possible while minimizing the risk of running short.  Basically there are three variations of the garter and stockinette stitch combo that can be worked:

20 rows:  6 rows of garter, 8 rows of stockinette, 6 rows of garter
16 rows:  4 rows of garter, 8 rows of stockinette, 4 rows of garter
14 rows:  4 rows of garter, 6 rows of stockinette, 4 rows of garter.

On the second side I will be keeping a row by row record of my yarn usage so I can determine a stitches per gram for both the garter and stockinette sections so that folks can figure out their approximate yarn usage depending upon how many rows they knit on the central panel.

I also have to provide a formula for determining how many stitches you need to keep for the opening to make sure that the shrug fits properly.  I'm thinking that it should be based upon the width of the shoulders plus the distance from the nape of the neck to the natural waist.

Pattern:  Traveling Zebra by Louise Robert
Yarn:  Bis-sock by Biscotte & Cie
Needle:  US 2.5 (3 mm) & US 4 (3.5 mm)