The Neck to Shoulder Length is crucial to making shifts, jackets, bodices, doublets, and basically any other garment with a fitted shoulder and/or a sleeve that sits at the point of the shoulder. If your Neck to Shoulder Length is off, your finished garments will always look droopy-in-the-shoulder (too long) or have that entirely unflattering Ack!-my-sleeves-are-attacking-my-head effect (too short). The first case, the drop shoulder, comes in and out of fashion, but the second is pretty universally regarded as a bad idea….
The Neck to Shoulder Length is taken along the top of the shoulder, where the front and back of the body meet. Neck to Shoulder Length is taken from the Neck out to the Shoulder Point (where the Armscye sits).
This measurement should be taken while standing in a normal posture, with your arms slightly out to the side of hanging comfortably – they should not be raised fully to shoulder level or higher, as this will affect the measurement. You can take this measurement yourself, if you can keep your shoulders relaxed. If you tense up, your measurement will be inaccurate. If your shoulders are imbalanced, due to athletics or some other physical consideration, you should measure both shoulders. Label these measurements, and be aware that you will need to draft each side of any garment that fits the shoulder. Also, if you are, say, working with a character who plans to portray a hunchback and requires a shoulder prosthesis on one side, you will ideally want to take a Neck to Shoulder Length measurement on both sides, with the prosthesis in place. (I mention this only because it’s happened to me…)