Garsault and math

I’m told that Garsault in the 18th C said you could add 6” to the back of a girls shift to lengthen it 6”. But, it will only lengthen it by 3.  (Slightly less, due to seams)

Edit: it’s actually only about 2.5” longer, due to seam allowances.  Blogspot won’t let me edit the post correctly try.

Method:
Remove the sleeves, leave the side seams and all intact.
Slice across the base of the neck on the front ONLY.  I cut 7” down from shoulders.

So, it’s 18” from shoulder fold to hem.
 Fold the flap up,  making it 25”, and 4” back down, creating a 6” gap for the new fabric, and it’s 21”

See? It’s 3” above the old shoulder fold (I have a seam as this is out of my scrap fabric), the cut edge is “ below that old shoulder, and 6 “ gap waiting to be filled.

See? 3” taller.

Sew in the new piece

Now the front is the back and the back is the front and it’s 3” longer.  Above is the new back. Below is the new front.