# Calculating Sweater Sleeve Decreases

Suppose I have a sweater pattern that I wish to modify so the arms fit me exactly.

First, I want to enter the data from my gauge swatch so I can do the right
calculations.  I like to take pictures of my washed and blocked swatches so I
have that data handy on my phone if I need it.

![Sweater Swatch: Rows](swatch-rows.png)
![Sweater Swatch: Stitches](swatch-stitches.png)

The original sweater pattern was 24 stitches and 18 rows for a 4x4 inch swatch,
but my row count didn't line up, so I know I'm going to be doing something
different than the original pattern.  Let's import what I've got into a swatch. 

```python
import pyknit
sweaterSwatch = pyknit.GaugeSwatch(row_count=18, row_measure=3.25, stitch_count=24, stitch_measure=4, units="in")
```

Then I can go measure the sleeve against my arm.  In this case, I already had the top of the sleeve because this was a raglan sweater and the directions called for 2 inches of straight knitting first.  I decide I want another 11 inches of sleeve.

```python
print(sweaterSwatch.measurement_to_rows(11))
61
```

Okay, so that's another 61 rows.  

Looking back at the pattern, I have a starting count of 59 stitches and want an ending count of 43.  (I check the measurement from the pattern diagram to see if I really want the sleeve that size, but it turns out that the sleeve width is fine so I'm not customizing it.)  This pattern uses a fairly common 2-stiches decreased in every decrease row pattern.  So let's enter that all into pyknit:

```python
print(pyknit.sleeve_decreases(61, starting_count=59, ending_count=43, decrease_per_row=2))
[decrease row, do 7 rows in pattern] * 5 times, [decrease row, do 6 rows in pattern] * 3 times
```

And there we have it!  

Let's double-check against my original pattern, though, just in case.  The original pattern had decreases every 9 rounds 8 times total.  We're still 8 times total, but because I wanted a shorter sleeve than the original pattern, I'm doing my decreases more frequently.  That all makes sense, so now it's time to knit!