With arms outstretched for all measurements, measure on back from left elbow to edge of left shoulder, this is measurement A. Measure on back from left elbow to edge of right shoulder, this is measurement B. Measure on back from elbow to elbow, this is measurement C.
Cast on 68 stitches. Work in Stockinette Stitch, decreasing at each edge every 8th row, until piece measures A. Place a stitch marker at each edge of this row. Work straight (no decreases) until piece measures B. Place a stitch marker at each edge of this row. Continue working in Stockinette Stitch, increases at each edge until piece measures C. Bind off loosely.
Sew seams together lengthwise from elbow to markers on side.