Knitting math (triangular shawls)
Wing o' the Moth is 65% done. How do I know? No, I didn't use the Excel shawl progress calculator. For one thing I hate Excel, spreadsheets and Microsoft software in general, and then I much rather prefer to be able to figure things out for myself. If I can do it on paper, I don't have to get up from the sofa (my knitting place of choice) and get back to the computer.
I had seen a blog post months ago about the math of calculating your knitting progress on triangular shawls, but I couldn't find it so I posted a request for help on Ravelry and sputnik provided the formula derived from the Excel progress calculator.
That went over my head (yeah, a math genius I'm not) so with what I remembered from the blog post I couldn't find and a couple of tries, I got this and it seems to work well.
Here it is:
Take your total numer of rows (in my case 204) and multiply by the total number of stitches at the longest row (471) and you get the total number of stitches your shawl requires.
Total rows = 204
Total sts at last (longest) row = 471
204 * 471 = 96,084
Divide that by 2 and you get the total number of stitches you need to knit to make the shawl.
96,084 / 2 = 48,042
Now take the number of rows you've knitted, say 165, and the number of stitches on the needle, about 385 (I may be off a couple of stitches but you get the idea) and do the same.
Multiply the current row by the current stitches, divide the result by two and you'll get the number of stitches you have knitted so far.
165 * 385 = 63,140 / 2 = 31,570
Now divide the current stitches by the total stitches to get your progress so far:
31,570 / 48,042 = 0.65 (65%)
To put this into a formula where CR = Current rows, Cs = Current stitches, TCs = Total Current stitches, Tr = Total rows, Ts = Total stitches, TOs = Total Overall stitches, P = progress:
(Cr * Cs) / 2 = TCs
(Tr * Ts) / 2 = TOs
TCs / TOs = P
As soon as I figured it out, madorville replied on Ravelry and pointed me to her own blog entry. Her system is more detailed and takes into account yarn weight.
…which goes to show that you never have to do anything, if you wait long enough.
Comments
Argh! I think I'm sticking to my own approximation method ... LOL!
Posted by: Agnes | September 20, 2007 7:02 PM
So there will soon be a finished shawl then :-)
Thanks for the formulas, saving some thinking for us others.
Posted by: Maud | September 20, 2007 9:19 PM
Looking forward to seeing the shawl, suspect I'd rather not do calculations on things like that!
Posted by: rosie | September 21, 2007 12:39 AM
Um, my head just exploded. My shawl calculator goes something like this:
Hmm. Looks about half done.
I call this the TLAR method: That Looks About Right.
Posted by: fleegle | September 21, 2007 3:12 AM
My head just exploded, too. I'm with Fleegle. I much prefer the guessing method myself. It's much more entertaining when it doesn't work out.
Posted by: Lorette | September 21, 2007 4:59 PM
I'm with Fleegle and Lorette! I'd probably be a better knitter if I didn't shy away from math.
Also, after years of working with Microsoft software on the job and suffering all the stupid software updates that are supposed to make life easier, but make it harder to accomplish tasks, I shudder when I think of how much time I wasted.
Posted by: domesticshorthair | September 22, 2007 10:04 AM
Hi Francesca,
I admire your patience showing us how to make this calculation. Next time, you might want to try the following short cut to calculate the proportion of the triangular shawl that you've completed. The underlying assumption here is that your gauge is constant and that the shawl pattern is uniform throughout. I assumed that the shawl shape is an isosceles right triangle, but I suspect that this formula will hold true for any isosceles triangle. The proportion of the shawl that is complete equals the square of the ratio of stitches that you now have on your needle to the target number of stitches. So for your example, it would be (385/471)^2, which yields 67%. I proved this formula to myself for an isosceles triangle; I didn't bother to do so for other triangles but I think that it will work. I always tell my boys that you really do use the geometry that they learn in middle school in everyday life, like knitting, but they aren't that impressed with my arguments. It might be because they see me rip-out parts of projects often enough to know that my calculations don't always save me work.-- Dan Schultz
Posted by: Daniel Schultz | September 24, 2007 8:38 AM
For a moment I had a glimmer of hope that you'd solved the fusty little decrease issue I'm having with a series of triangular shawls. My brain simply hasn't been in math mode for weeks so the projects languish on the couch, taunting me.
More chocolate, perhaps...
I have a dear friend who does the math for astrology charts on paper and in her head. Mental knitting of a sort. She's a computer expert, but like you enjoys curling up on the couch with paper and pencil.
Posted by: Sylvia | September 25, 2007 9:41 AM