An update on the shawl calculations. We aren't knitting triangles, we are knitting trapezoids! That explains the formula Susan and I each derived.
Recall from Algebra I: Area of trapezoid is 1/2(Base1 + Base2)*Height
In our cases, remember N = number of rows
Base1 = 7 stitches
Base2 = 2N+3 stitches
Height = N
voila! Number of Stitches = N² + 5N
Oh, why didn't I do this immediately instead of working out the sum from i = 0 to N of (7 + 2i)? Just goes to show that too much mathematics is a dangerous thing.
Kmkat, the Gaussian addition thing is from a (probably apocryphal) story of little smart ass future famous mathematician Gauss as a child and a teacher who was fed up and wanted some peace and quiet. She asked the class to sit quietly and add all the integers from 1 to 100. Gauss figured out almost immediately that the answer was 5,050. So much for the teacher's quiet afternoon.
As for me and my shawl last night I completed pattern repeat number 11. According to my calculations, I have knit 74.4% of the shawl and according to my scale I have used 73.8% of the yarn! It will be close. That's using the 12 repeats/88 grams. Have to admit I am tempted to work some more on untangling the 12 grams and adding an extra repeat. If all goes well, if I can manage to untangle the whole thing, I can complete 13 pattern repeats and end up with about 2 or 3 grams left over.