Broad Street Mittens -- Sleeve

I've now knitted one pair of Janis Cortese's Broad Street Mittens in worsted yarn. They fit nicely, but, unfortunately, only come to my wrist as I've not yet started knitting the cuff/sleeve.

I want the sleeve to be at least 30 cm, so left it out of knitting the mittens until I saw how they turned out. Though, I suppose that I could have started with the sleeve and converted it into arm warmers after the fact.

I know that the current cuff of the mittens is 40 stitches around. I also know that my wrist is tiny, so what I intend to do is reduce to 30 stitches around (I pulled the cuff of the glove tight and counted the number of stitches around my wrist) and then add 5 stitches halfway up my arm.

Why 5? Well, I've found myself knitting a lot of k2p2 rib recently, so want to do something different, especially seeing as it looks serviceable but ultimately uninteresting when worked in multiple colours. I have a nice olive drab yarn that I bought when I was first considering these mittens, and I'd like the sleeves to be striped.

With those two constraints in mind, I considered various ribbings and decided that I'd work the following pattern:

1. knit 1, slip 1 purlwise with yarn in back, knit 1, purl 2 (repeat from start)
2. knit 3, purl 2 (repeat from start)

That way, the slipped stitches break the monotony of simple circular stripes, forming a slight wave pattern with the purl stitches, while still providing the texture and stretchiness of ribbing.

The final consideration is what gauge to use. I'd considered knitting the sleeve on 3.75mm needles, but gradually decided that, since it's a layer that will be worn along with a shirt and coat, that I might be wise to use 5mm needles to get a looser fabric. That means that, rather than using 30 stitches as I'd intended, I'll need to use fewer.

My gauge on the gloves was 8 stitches / inch and my gauge on the 5mm needles with worsted yarn is 5 stitches/inch. From there, it's simple algebra to figure out how many I need:

desired stitches / 30 == 5 st/in / 8 st/in

desired stitches == ( 5 / 8 ) * 30

desired stitches = 18.75

Since the pattern I'm using for the ribbing is a repeat of 5 stitches, I round 18.75 to 20 and know that I need to decrease half the stitches to make it fit. In order to keep the glove from puffing out, I'm going to try picking up 40 stitches then decreasing ten of them the next row, knitting one row straight, then decreasing ten times on the next row.

If that doesn't work, I'll rip it out, pick up and knit a round with 3.75mm needles, decrease to 30 stitches and then knit onto the 5mm needles.

A note, though: to keep the fabric from stretching as I pick up, that will be done on 3.75mm needles and the second round will be knit onto the 5mm ones.