Annie has given me permission to include her sizing tips on our KAL. Here goes:
"For final garment size, measure yourself at 2 points:
A) Across your front, from armhole to armhold if you're wearing a top with sleeves. Divide the cross front meas by .83 to determine armhole placement.
B) From fingertip to fingertip with spread arms. Divide tip to tip measurement by 1.73 to determine final garment circ."
Surely Annie means the final garment's diameter above, how wide it is across. I don't know why we are to divide by these particular numbers, but I'll take Annie's word for it. :)