ok, I stink at math but am trying to learn “knitting math” which sounds much more agreeable to me! Sooooo…I’ll take a stab at sounding foolish here!
So you have your cup measurements. You have to figure out your yarn gauge and swatch. What yarn are you using, skinny little lace weight where you get 200 stitches to an inch or a big ol’ fatty yarn where you get 4 stitches to an inch? (Little humor there since we’re talking math) Then divide your # of stitches into your measurements to decide how many to cast on (top down or bottom up?) You also have to figure out how many rows (based on your swatch) it will take to get your length for the cozy. # of rows divided into length of cup.
THEN you have to figure the decreases (or increases, depending on which way you are knitting) by subtracting the bottom circumference from the top (so 2" in this case) and figure out how to decrease 2" even over how many rows it takes for you to knit the total length of 3 1/2"…
Clear as mud? Please, someone else, clarify!!
Good luck! But if all else fails…http://www.knitty.com/ISSUEwinter06/PATTslingshot.html
this is a jumping point?!