To understand what on earth I am talking about in this post you will have to get your copy of Metric Pattern Cutting out and turn to pages 16 and 17.
Anyway, the adaptions I made to the method are these:
Centre Back Length:
0 -- 5: Full back length
5 --1 = centre back length ( gives much better fit at the back neck).
Back Shoulder Slope/Pitch/Squareness:
To get the shoulders the right amount of slope, use your ruler as a giant drafting compass from 5 to draft an arch for the shoulder pitch. To get the shoulder point do similar thing from 9 using the shoulder length plus 1cm for a dart.
0 -- 2 = Armscye Depth + 2cm (I used the standard measurement).
Centre Front Length:
For front length go down from 4 the full front length measurement and mark "x". Measure up from x the centre front length. This gives a more comfortable neckline. 20-27 = DART WIDTH. 20-26 is bust depth marked along the dotted line.
Front Shoulder Slope/Pitch/Squareness:
The shoulder is drawn much like the back shoulder was, but using 27 as the neck point. For the pitch, go up from x to the bust point and then use the bust point as the pivot point. Arch from 27 the shoulder length. Where the arches cross is the shoulder point. On my new sloper it is level with the back shoulder point even though my front pitch is 2cm longer than my back pitch.
Divide 29-22 in half and mark. Connect the point and 32 straight. Slide your square along this line until its arm hits 22. Connect straight, divide into 3 and mark the point nearest 22. Curve from 30 to half-point to third-point to 32.
Repeat for the back armscye except that you use the third-point further from 14. You will probably have to draw these curves by hand (i.e. without a french curve).
12cm shaping is not going to work for everybody. The amount you need to take the waist in will of course depend on how small it is compared with your bust, i.e.
(bust + ease of 10cm) - (waist + ease of 6cm)
(79+10cm)-(60+6cm) = 23cm, divided by 2 (for a half-a-person pattern) =11.5cm
Then divided that by 3 (=3.8). We'll call this w.
For the front waist dart you add 0.5cm to this. 3.8 + 0.5 = 4.3cm
For the front side shaping (i.e. how much you take the side seam in at the front) you divide w by 2 and add 0.5. 3.8 / 2 = 1.9cm, + 0.5 = 2.4cm
The back side-seam shaping is w/2 - 0.5cm: 3.8cm/2 -0.5cm = 0.9cm.
The back dart is ((w - 0.5cm)/3) x 2 : ((3.8cm-0.5cm)/3) x 2 = (3.3/3 = 1.1) x 2 = 2.2cm
The centre back waist shaping is (w - 0.5cm)/3: 3.3/3 = 1.1cm
I think the CB shaping helps avoid swayback misdiagnosis. This is like a dart that is in a seam so you must still leave the original drawn CB line for when you add extend down to the hip line. Once you have tried this CB shaping I think you will be very pleased with the difference it makes to your dresses and tops.
(12th July 3013) UPDATE:
The standard proportion of waist shaping show above doesn't work for everybody (me) because some people have more shaping at the back than at the front. Therefore a better, more personalised way is needed, and this is how I do it:
Subtract a quarter of the waist+ease measurement (Here 66 divided by 4 = 16.5cm) from the front bust-line meausurement (3--32 on the above drawing) and call this F. Divide F by three and call this f. The front dart is 2f (so you can just measure out f from the front waist dart line), and the front side waist shaping is f. That's the front waist done.
The back shaping is done like this:
Subtract a quarter of the waist+ease measurement (16.5cm) from the back bustline measurement (here line 2--22). Call this B. The back waist dart is 0.5B. The CB shaping is 0.2B. The side seam shaping is 0.3B. If you like you can probably equalize the side seam shaping.
The darts are extended 3/4 waist to hip (on me 3/4 20cm = 15cm).
The back hips should also be bigger than the front hips. This makes a real difference to the hang of the garment when it's unbuttoned (like a dressmaker summer jacket). It you have the pattern's back hips too narrow and the front hips too wide, you will find the garment swings open when unbuttoned and when it's closed, the front will have flare and the back will bubble up above the hem; it won't be smooth.
So you see, the garment swinging open is not always because of the shoulders or bust. They might be fitted perfectly but the garment still swings. To find out how much bigger your back hips should be compared with your front hips, have the tape measure around your hips with the start at where you feel your side seam should be and the lower numbers to your front. Put your finger nail on the other imaginary side seam and, taking care to keep the measurement "marked", remove the tape measure. Now you have your front hip measurement and your full hip measurement. Take your front hips from your full hips and you have your back hip measurement. (It's worth noting these down by the way).
Divide this measurement in two.
Suppose the full hip measurement were 88cm and the front hips were 43cm. That means the back hips are 45cm. The pattern will use half-measurements so we have:
Full hips: 44cm
Front hips: 21.5cm
Back hips: 22.5cm.
This means that for the pattern's sake we have a difference of 22.5cm-21.5cm=1cm difference between the front and back hips (2cm in real life). So even after ease has been added the hip measurement, and that number divided in four for the front and back patterns, we add 0.5cm to the back hips and take 0.5cm from the front hips for a difference of 1cm on the pattern.
88cm + 6cm ease = 94cm
94cm / 4 = 23.5cm
Front: 23.5cm - 0.5cm = 23cm
Back: 23.5cm + 0.5cm = 24cm
Difference = 1cm on the half-a-person pattern, total 2cm difference in real life.
I think these adaptions should avoid many fitting problems, but I would love to know what you think. If you have blogged about it, please add a link in a comment below and (as long as it's not spam) I'll enable the comment (comments with links seem to go straight to spam).