How to: increase evenly along a row using Excel

Last week I revealed my embarrassing struggles to figure out the completely standard problem of how to calculate sleeve shaping. (I console myself with the knowledge that my extremely smart friend Claire, who has a PhD in astrophysics and teaches university maths, confesses herself scared of knitting maths. It's slippery stuff, is knitting maths.) 

Today, as promised, I'll show you the other thing I recently had to figure out from first principles: how to use Excel to spread increases out evenly along a single row – as often happens, for instance, when switching from a border pattern (like ribbing) to the main body pattern. I'm a control freak and tend to work these increases into the stitch pattern itself – I doubt I'd ever write simply "increase 13 sts evenly along Row 1", but it is a fairly common instruction, especially in older patterns. If you're faced with an instruction like this, it's really okay to just fudge it; take a guesstimate and slap the increases in, say, every 3 or 4 stitches as the mood takes you, counting them up towards the end of the row and adjusting accordingly. As long as you know roughly how the increases divide into your total stitch count, you're more than likely to get a fairly even result. But if you're a control freak like me, you can work it out exactly – and if you want to write a pattern for a range of sizes, and avoid that vague instruction, you can use Excel, thusly.

Before we start, you need these figures:
SC: starting stitch count
DC: desired stitch count
IC: the increase count, ie difference between SC and DC.
Note: if working flat, make sure you don't include your edge stitches in these counts. 

Example numbers:
SC = 56
DC = 78
IC = 22

First, understand the problem. In most cases of course your starting stitch count won't divide neatly by your increase count and you'll be left with a possibly large remainder – the extra stitches left at the end of the row if you rounded down your increase interval to the next whole number. (For instance, 56/22 gives you a remainder of 12.) With sleeve shaping, I spread those extra rows out over the bottom of the sleeve, slightly lengthening the decrease intervals and reducing the slope of that portion. But this time, I don't particularly want to have all my extra stitches lopsidedly spread out on one side of a single row – I want them spread evenly across the row.

To achieve this, I plan to alternate between two different increase intervals (the basic interval, and that interval plus one of the "remainder" stitches). Ie, my pattern will have an instruction to repeat "m1, kA, m1, kB".

So let's get started.

1. Halve IC (HC) to find out how many increase repeats we need – how many times we'll work that "m1, kA, m1, kB" repeat. 

Excel formula: =IC/2
Example: 22/2=11

2. Divide the starting count by this halved increase count. This gives you the number of total stitches in each increase repeat; call it total repeat, or TR. 

Excel formula: =SC/HC
Example: 56/11=5

3. Within each of these repeats you need to increase two stitches. So halve TR and round up and down to get your higher and lower increase intervals (HI and LI), respectively – ie the number of whole stitches between increases. If TR is an even number, HI and LI will be equal.

Excel formulas: =ROUNDUP(TR/2,0) and =ROUNDDOWN(TR/2,0)
Note: the 0 means that we are rounding to zero decimal points.
Example: 2 and 3

4. Time to see what's left over if we work this repeat along the row – the remainder (RM).

Excel formula: =MOD(SC/HC) 
Example: 56/11 leaves a remainder of 1.

5. Stick this number at the very start of your row or round, and you're done! 

Your pattern instructions will look like this (assuming a plain knit row):

K RM, (m1, LI, m1, HI) to end.
Example: K1, (m1, k2, m1, k3) to end.

Bonus tip: If you have a reasonably sized remainder, you could take a few of those stitches over to the end of your row, for better balance. It's not practical to include instructions for that in a multiple-sizes pattern, though. 

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