Similar to a FBA, the SBA is equally not as difficult nor should it be scary.
You'll want to consider a small bust adjustment if you are smaller than a B cup, if your waist and hip measurement put you at one size but your bust measurement puts you at a different size, or if you've completed a muslin draft of the original pattern and find that the bust dart is giving your body a shape it's didn't acquire on its on!
Let's get started. The first steps of this process are similar to the FBA. Later you'll see where we break away into unique only to SBA territory!
Get your measuring tape out, some marking utensils, scissors, tape, a ruler and let's get started!
FIND YOUR ADJUSTMENT
Figure out what size you would work if you used your bust measurement. Compare that to what size you would use for your other measurements. On the pattern print out, measure the distance between the sizes and that will be your small bust adjustment.
1. Draw and extended a line through the center of the dart and 1 inch past the dart point. This mark will indicate the bust point.
2. Draw a line from the dot marking on the arms syce to the bust point.
3. Draw a line parallel to the grain line marking on the bodice from the bust point to the hem.
4. Draw a line perpendicular to and halfway down the length of the previous line and to the center fold line of the bodice.
Cut line 3 and through along 2 leaving a small bit of paper at the arm syce edge as a hinge.
Next, cut along line 1 towards the bust apex, leaving a small bit of paper at the bust apex to use as a hinge.
Now, we'll take our bust adjustment measurement and make a few indications on the bodice from the vertical cut line and in towards the centerline.
<Notice how the picture tone changed? This is where we break away from the same steps as the FBA and go on into new SBA territory>
Time to overlap the slash lines the measured distance. Ensure the slash lines stay parallel.
Tape the bodice in place above the 4th slash line. Then cut through the 4th slash line so we can even up the base of the bodice.
Now, overlap the 4th slash line over itself until the base edge of the bodice matches up. Secure in place with tape.
Time to redraw the dart lines. Unfortunately, I placed my other dart line behind the pattern piece so it was hard to find. Don't be like me. ;)
And there you have it! You're new bodice, altered to your personal measurements and unique to you!