Originally Published in Knitter’s 9, Winter 1987, and listed as the The Π Shawl. From the Shawls & Scarves book (and probably from the original publication as well):

“Make it simple. For many knitters, this shawl has been an introduction to lace knitting and to the knitting of circular things. And a good choice it is. The lace patterns are not too difficult, and the circle’s shaping is simpler yet. But all can be even simpler.”
-Elizabeth Zimmermann

Yardage is not listed, weight is given as follows:
“9 oz fingering- (or 12oz sport-) weight Shetland wool”

From the Knitter’s Almanac (July) book:

Summary: A circular shawl based the geometry of Pi--the relationship between a circle’s circumference and its radius containing six shaping rounds.

Additional Information:

GAUGE: about 3 sts to 1” (should be a very loose GAUGE)

MATERIALS: 3-4 4oz wheels single-ply Icelandic wool. 10-12 oz Shetland wool, or approximate amount of any yarn which works up at above GAUGE.

1 set sock needles, 1 16”, 1 24” circular needle of a size to give above GAUGE. Approx. #7-#10 1/2

This month’s chapter includes directions for 2 shawls, this and one with Concentric Circles of Holes made with faux increase rows. Both shawls are essentially the same, but differ in the decorative details.

This month also includes directions for a one row, 3 stitch button hole.

Elizabeth Zimmermann’s elaboration on the Pi Shawl:

“When you set out on the annual family trip naturally you have to take your knitting; something has to keep you sane in face of the possibly quite ferocious situations you will be up against in the next two weeks.

Try a shawl.

I have a circular shawl for you which starts at the center, has absolutely no pattern, and only six shaping-rounds in the whole thing.“

From the back of the book:

“The year begins with an Aran sweater and proceeds to February baby things, a March Shetland, April blanket, May mittens and so on through the months, completing the zodiac with November moccasin socks and a December last-minute wishbone sweater.”

Errata link is for the version that appeared in “The Best of Knitters: Shawls & Scarves” book. Follow the link then download the PDF.