When a fitting change crosses a design feature, says fitting expert Karen Howland, ask yourself what the pattern piece looked like before the feature was added.
Designers usually make their changes to a basic fitting pattern called a sloper.
For example, if you needed to change the shoulder slope or length on a blouse with front tucks, as shown at right, you'd naturally want to fold out the tucks before you reshaped the shoulder seam. The sleeve you described, shown in the first drawing below, isn't much more complex than that. It certainly appears to have been derived from a basic one-piece fitted sleeve sloper. In this example, a one-piece sleeve with pleats in the sleeve cap needs lengthening at the cap. To make the simple alteration, first fold out the pleat details to return the sleeve to the shape of the original sloper it came from.