A while back, I described several ways of altering Silver Streak in order to make it into a shorter cardigan. At that point, I simply discussed how one might go about modifying the length, but didn’t explain how to calculate even spaced decreases or increases.
Knowing how to adjust length is you first tool towards custom fitting your knitwear – patterns are written with an average size in mind and while the circumference may fit you with nary an adjustment, you’ll want to adjust some length if you’re shorter or taller than 5’6″.
Before you can begin to calculate your increases or decreases (the formula is the same for both), you need to translate your length into rows. Let’s take a simple sleeve as our example: we intend for it be 19″ long and our row gauge is 7.5sts/1″, therefore we’ll need 142 rows to complete it (it really was 142.5 rows but we knitters prefer even numbers). We need to work even for about an half an inch before binding off, so lets take off 6 rows to bring down the number of rows to 136. This will be our dividend or ‘A’.
This sleeve begins with 60 sts at the wrist and increases to 88 sts at the bicep for a difference of 28 sts. Since the increases will be worked in pairs, however, we need to divide this number in two to obtain the number by which to increase – 14. This will be our divisor or ‘B’.
Easy enough so far. The next part is what I can never remember by myself – others keep notes for working the kitchener stitch, I keep notes on this. You’ll probably find it helpful to add tags such as I do here (A, B, C, etc) if you’re anything like me. Once you understand the concept, the illustration above will suffice.
First, divide A by B: 136/14=9.7 (‘C’)
Had C been a whole number(such as it would have been had you started with 126 instead of 136), you’d have no need for further calculations and could simply increase every 9 rows. I know what you’re thinking: every 9 rows?!? Don’t worry, we’ll talk about how to obtain nice, even numbers in a minute.
Second, multiply B by C: 14*9=126 (‘D’)
Third, subtract D from A: 136-126=10 (‘E’)
Fourth, subtract E from B: 14-10=4 (‘F’)
Finally, here are our results:
Increase on every 10(C+1)rows 10(E)times
Increase on every 9(C)rows 4(F)times
Again, the result would have us work increases every 9 rows. In order to obtain increases only on right side rows, we need to run the calculation in a somewhat modified manner by halving A and doubling ‘C+1′ and ‘C’ in the results:
Increase on every 5(C+1)rows 12(E)times
Increase on every 4(C)rows 2(F)times
Double the results from ‘C+1′ and ‘C’, and we end up with ‘increase on every 10th row 12 times and on every foll 8th row 2 times’
That’s it. Next time you’re planning a sweater, take a few minutes to compare its schematic against a sweater that fits you well and make adjustments as needed. It only takes a few minutes and you’ll soon be custom fitting every sweater you knit.