This section is from the book "Clothing For Women: Selection, Design, Construction", by Laura I. Baldt. Also available from Amazon: Clothing For Women: Selection, Design, Construction.
See Fig. 38 for suggestion. Place the cut ends of the muslin together.
Fold the selvedge edge of one thickness of material over from the opposite side far enough to place the. center back on the fold, and allow plenty of seams. Or, place center back one-quarter inch from selvedge, and use seam center back, which is allowable in testing pattern.
Place patterns so lengthwise threads run around the neck and arm. Cut only one thickness of each.
Fig. 38 - Shirtwaist pattern placed on cambric or muslin, ready for cutting a trial waist.
As there are usually no seams allowed on drafted patterns, it will be necessary to make this allowance when cutting. Waist, allow one-inch seam on shoulder and underarm; one-quarter-inch at neck and armhole; nothing at the bottom. Sleeve, allow one inch on length seams and three-eighths inch at top and bottom. Neck band and cuff, one-quarter inch. Do not mark the seam allowance, but learn to use your tape measure, passing it along the edge of the seam at the required allowance, and cutting along the outer end of the measure. This will help to train your eye for distance, and give you assurance. Later, you will be able to cut accurately without even this guide. Lay aside all pieces left from cutting.
-It is more orderly to cut all the pieces of the pattern, then trace the seams. Waist: Trace waist, neck and arm-hole lines first, then the shoulder, center of shoulder, and the underarm seam, beginning at the waist line and tracing up and down along edge of pattern. Sleeve: Trace length seams, also top and bottom, along edge of pattern. Collar Band and Cuff: Trace all around edges of pattern.
To baste for fitting (Fig. 184), mark waist, neck and armhole lines with colored thread; also center, back and front lines, and center of shoulder. Turn right-hand side of front on center line and baste. Underarm Seam: Have waist and armhole lines meet; pin seam (pins at right angles to seam), keeping traced lines together. Baste from waist line up and down, using small stitches. Shoulder Seam: Hold back shoulder toward you while basting. Have neck lines, armhole lines and center shoulders meet. Ease the fulness of the back into the front shoulder. Baste seam of sleeve. The collar band and sleeve are not placed until after the first fitting.