Last seen on: Secret Project, with math!

**For**: Jan & Sara, just married in June.

**Pattern**: Jasper’s Chevron Blankie

(errata: “SK 3 ST” in R2 and every subsequent row should be “SK 4 ST” otherwise the gaps won’t be centered over each other.)

It’s not big enough for two people (which a friend pointed out doesn’t make it a very unity-inspiring wedding gift) but it’s perfect for one person to snuggle under for a nap. One or the other of them now, and maybe someday some adorable mini-Jan or mini-Sara.

Or some handsome cats.

I’ve been looking over the math that I did before committing to making the blanket. It’s rife with bad lab practices – bad assumptions as shortcuts, dropping significant figures, rounding up or down for convenience – and it’s no surprise that the amount of yarn I predicted I’d have left over after finishing wasn’t all that close to what I ended up with.

To be fair, I did finish the blanket without running out of yarn, which is what I did all the math for in the first place. But, for example, I predicted I’d be left with 39g of blue yarn, whereas I actually only have 7g left. Yes, that last row of blue was a bit nerve wracking.

More weirdly, I thought I’d have 124g of the red left, but it turns out I still have 162g.

The biggest error I made, all the way back at the beginning, was taking my swatch, which had 4 rows of red, 4 rows of grey, and 1 row of blue, and extrapolating it out to a blanket that was proportionally 4 grey to 4 red to TWO blue rows. I doubled the amount of blue in the blanket while making the assumption that this extra yarn wouldn’t change the density of the overall fabric and that all the yarns had the same exact weight. I knew that wasn’t true, but I didn’t realize how significantly that difference would play out over the large size of the piece.

Earlier tonight, I tested this, weighing out 5 grams of each yarn before laying them down on the floor and seeing how much length there was per unit. The grey yarn was 74 cm longer than the blue and the red was 110cm longer than the blue. The weight of the blue, which was more than 1/9 of the weight of the swatch, caused me to overestimate how much of the grey and red I’d use and thus also underestimate how much of the blue I’d use.

The only thing I came kind of close on was getting the final weight of the blanket correct. I’d estimated 1073g and in reality the blanket came out to 987g. That’s only 8% error. Not *too* bad…

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thegelfling

said:It sounds like the swatch and the weight assumption is where most of the error came from, not dropping significant figures and rounding. Remember, gravity is exactly 10!