To start, you need to know your side to side chest measurement and your side to side back measurement. Mine is 14" in the front and 14 1/2" in the back.
The pattern above is of a back. To compare the pattern measurements to my body measurements, I measure from center back to the small circle for my size. This circle...
... is almost always drawn on the pattern but if it's not, you'll know from other patterns about where it's positioned. For me, the measurement from center back to this circle needs to be 7 1/4" or half of 14 1/2". Whatever the difference is, that is the amount of the narrow back adjustment I'll make. It differs pattern to pattern however, the amount of the adjustment needs to be the same in the front and the back otherwise one edge will need to be eased. I've never had that issue. I've always made the same adjustment front and back.
I recently traced Marcy Tilton's Vogue 9089. This design has a button band. In order to measure from center front to the small dot, I overlapped the two pattern pieces and pinned them together.
Aligning the edge of the ruler with center front, I measured straight across to the small dot.
The distance is 7 3/4". For me, the distance from center front to the dot needs to be 7" so I will make a 3/4" narrow chest adjustment. To do that...
... I start by drawing a box around the armhole using the grainline to keep these lines parallel to or at a ninety-degree angle from the grainline. Above, I first drew the box and then drew another parallel line 3/4" away for the narrow shoulder adjustment.
Next, I cut across from the armhole and fold the two parallel lines together. This lengthens the space from the side seam to the front (or back) notch by the amount of the adjustment or 3/4" in this case. I'll add 3/4" to each side of the sleeve or 1 1/2" in total which can make the difference between a far too tight and a just right bicep width.
Next, you shape the shoulder seam. At one point, I drew the new shoulder line from the lowered shoulder point to the original neck point only had problems with pulling at the shoulders. A friend who is a professional seamstress suggested I should raise the shoulder point 1/4" which seemed strange because I didn't think of myself as having square shoulders and then I realized that I also didn't have sloped shoulders which is the adjustment that happened when I connected the neck and new shoulder points. Now, I extend the original line. As you can see above, that - along with the 3/4" adjustment - adds to the cap height.
I don't make any adjustments to the sleeve until after I've made all of the adjustments to the front and back pieces. Along with the narrow chest and narrow back adjustments and extending the original shoulder line, I will need to check to see if the underarm should be raised. Looking at the shape above, I think that's most likely what will happen and all of these adjustments affect the cap height. I work through the adjustments step by step to get to the sleeve with the greatest possibility of success and then - with so many adjustments - I typically make a muslin sleeve when testing a new pattern just to be sure.
If you have narrow shoulders, it is quite possible that you - like me - need more than a narrow shoulder adjustment and might find the narrow chest and narrow back adjustments solve some of your fitting issues. It has really worked for me with the bonus of a much easier way to increase bicep width than other options. Let me know what you think.
Today... I have no appointments. After journal writing and walking Miss Chloe, I intend to spend the entire day in the studio working on pieces for my cruise collection. YES YES
Talk soon - Myrna
Grateful - sharing
If you have a candle, the light won't glow any dimmer if I light yours off of mine.
- Steven Tyler