Use this method to ensure that the extra hem allowance volume will remain flat on a curved hem, e.g. on a full skirt or a rounded slit, etc. With large stitches, machine-stitch two lines of stitching along the longer side of the hem edge. Baste hem allowance in position inwards und then carefully pull the lower thread of the stitched lines until the hem allowance lies flat. Evenly spread out the gathering and press in position. Then neaten/finish the hem allowance and slip stitch the hem by hand or machine topstitch.