Fit comments are a language of their own. They are written fast, often by someone standing in a fitting room holding a measuring tape in one hand and a garment in the other. They are precise in the way they name body regions, but they assume you know what the correction means geometrically. Here is a short translation guide.
"Drop the armhole X cm"
This means the armhole depth needs to increase by X cm — the lowest point of the armhole (the underarm point) should move down toward the hem. You achieve this by extending the side seam at the underarm. The sleeve cap height must also increase by the same amount, otherwise the sleeve will twist forward at the shoulder. Always adjust both the body and the sleeve together.
"Take in at the side seam"
The garment is too wide at the body, and the correction is symmetric: remove equal amounts from the front and back side seam. If the comment specifies "at the waist" or "at the hip," it is asking for a shaped seam, not a straight take-in. Mark the callout point clearly on your corrected pattern and check that the front and back pieces still have matching seam lengths.
"The shoulder seam is sitting forward"
This is a rotation issue. The shoulder seam, which should sit at the top of the shoulder, is rolling toward the front of the body. The fix is to rotate the sleeve cap forward at the attachment point, or to remove a small wedge from the back shoulder and add it to the front. The amount is usually 0.5–1 cm. It sounds small, but it changes the whole hang of the sleeve.
"The neckline is gaping"
The neckline opening is too large, or the neckband is too long relative to the opening it is meant to finish. If the fabric at the neck is flat, the issue is the opening itself — reduce it by taking out small, equal amounts from the front and back neck curves. If the rib is applied and it is gaping, the rib is not stretched enough during application — shorten the rib cut length, not the neck opening.
The key skill in reading fit comments is understanding which piece carries the correction. Fit comments describe symptoms on the body. Your job is to translate those symptoms into pattern adjustments.