Devere’s Drafting Formula
One of the more difficult concepts to understand is how Devere varied the size of a pattern. He used a size 18 3/4 breast as the basis for all of his patterns, which is equivalent to a 37 1/2 chest. This is called the proportionate model. If you are lucky enough to have a 37 1/2 chest (and the other corresponding measurements are the same), you can draft the patterns as they are straight from the book, with a normal ruler . Unfortunately, very few people fit these measurements, so adjustments have to be made.
Let us suppose we have a gentleman with a 42 inch chest, and want to find the correct balance for a coat. On a 37 1/2 inch proportionate model, the balance is 2 1/2. But a 42 inch chest would make that larger. First, you need to find the correct ratio between the 42 inch chest, and the proportionate chest. That would look like this:
42 / 37.5 = 1.12
After getting the number of 1.12, we multiply that by the balance measurement (or whatever measurement we need to get):
1.12 * 2.5 = 2.8
Then, it’s a matter of converting that 2.8 decimal into inches. This comes out to somewhere between 2 3/4 and 2 7/8. As you can see, this method is not very accurate, and prone to mathematical errors. And it takes a long time when you have to do 20 or 30 measurements this way.
Luckily, Devere was a fairly smart guy. He devised a set of rulers, called Graduated Rulers. The graduated rulers are, “a series of measures, which are successively graduated larger and smaller than the common inch measure, and are used to draft patterns for larger or smaller sizes than the 18 3/4 breast.” What does this mean? Instead of doing those calculations above, you simply choose a correct sized ruler and then draft the pattern as it is in the book.
When drafting trousers, the ruler size is taken from your seat measurement, rather than the chest.
Devere’s Graduated Rulers
For example, you are measuring someone and they have a 48 inch chest. You would then go to your set of rulers and choose the one marked size 48 (or 24 inch breast). If you compared this to a normal inch ruler, you would see that it is a lot larger, yet it still has 12 inches to it.
Where can you get these rulers? In Devere’s time, these rulers could be obtained from Devere’s company, and came on paper, tapes, or on wooden rulers. Devere has long gone out of business, but luckily, the rulers are not too difficult to make yourself. I’ll save you that trouble though.
I have created a set of graduated rulers, sized 34 through 50, for your convenience. They are on 11 x 17 inch paper, so you’ll need to find a print shop to print these. They can usually be printed for a few dollars on nice card stock at stores with print shops such as Staples. They are in Adobe pdf format. When printing from Adobe Acrobat Reader or other readers, be absolutely sure to set Page Scaling to None. If this is not done, your whole set of rulers will be off. After they are printed, I would take a normal inch ruler and compare it to the size 37 1/2 graduated ruler. They should be exactly the same. If they are off, it was printed incorrectly, and you’ll need to check your settings and try again.
|Read about Devere's system.|
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