Monday, June 4, 2012

Math Challenge: Moulage Class with Kenneth D. King / Day One

To: 
all math geniuses, 
anyone with IQ over 140, 
nerds,
pattern-making experts

Subject: "Why are you still using inches in the US???" or "solve the problem!"

Yes, it is a Moulage Class review. But I won't tell you anything about it before we resolve this mathematic problem.



(Ok, I will talk about the class a little bit: Twenty-four measurements, fraction orgy, foggy brains and five hours later, and we walked out with a custom draft of the back bodice for Kenneth D. King's Moulage Class. The class is great - fitting and patternmaking bootcamp! but...)

Back to inches! Dividing fractions is (to certain extent) masochistic. You disagree? I mean it takes just a second to divide two-digit numbers in metric system! Now do the same in inches... Piece of cake? yeah, right... Now, try to use fractions for patternmaking / calculations. It can't be as accurate as the metric system.

Here is the very first measurement we took: my neck, which, by the way, measures 13" (or 33cm). To draft the moulage, we need to make the following calculation:

1. Neck: 1/6 (neck measurement) + 1/2  = back neck

let's write it out: 1/6 x 13" + 1/2 = 2 1/6 + 1/2 = 2 2/3 (here, try now and get it converted to eights or sixteenths for the ruler units). My calculation was somewhere around 2 5/8 (it is a millimeter more, but there is no way you can get this so precise for inches ruler)

NOW, LET'S DO THE SAME IN CENTIMETERS

neck measurement : 6 + 0.5 

to remind you, my neck measurement is 13" = 33 cm

33 : 6 + 0.5 =   5.5 + 0.5 = 6 cm

Now, look at your measuring band if it contains both, inches and centimeters. You will see that these two calculations differ from each other in slightly more than 1/4" (or appr. 7 mm). 

Or, am I doing something wrong??? Yes? Then, here is your challenge: prove me wrong! (and don't think of me as another arrogant European, please! I am neutral)


EDIT: Reader Jilly B found the missing 7 mm (read her comment after you found the mistake in my calculations). Thanks, Jilly B!

But my question still remains, am I the only one who thinks that fraction calculations are extremely cumbersome in comparison? 

21 comments:

  1. Aha!!!   I was scratching my head on this one; then the light bulb went on.  It's in the step where you add 1/2, or .5    When you use the inches calculation, you are adding half an inch.   When you use the cm calculation, you are adding half a centimeter.  Everything is off after that.   Which are you supposed to add?   Half a cm or half an inch?

    And thank you - I'm not a nerd by any stretch of the imagination, but occasionally I do enjoy a good brain teaser.   (IF I can figure it out lol)

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  2. Yes inches are outdated. I came to this conclusion several years ago while  drafting a pattern jacket for class and it said use centimeters. I did and my life was never the same.
    Jilly Be you should ad the centimeter equivalent of half an inch. Half a centimeter won't be the same

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  3. Thanks Marina - do I go to the head of the class or something now?  ;-D   

    In response to your other question, I thought the U.S. was going metric years ago, but it never happened (don't get me started on stubborn old patriarchal attitudes.....)   I totally agree that a math system based on 10 is WAY easier than one dealing with 1/8's & 1/3's & ridiculous lengths like 5280 feet in a mile (Huh???)

    It's not easy to change a lifetime of habits, but it would sure be helpful if there were some more support!

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  4. If you have to do math then yes metric is easier. But measuring in metric is a nightmare when your eyesight starts to go. The mm are just way too close together. That level of precision is lost anyway if like me your sewing (and/or measuring) are less than perfect!

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  5. I am a metric-affectionate former science student, but also an American who has been thinking in imperial since she was born and hasn't had much opportunity to absorb metric. Right now I am still in school where we use inches because that's what our instructors and textbooks and commercial patterns used. But I recently got an interesting perspective on this talking to a Canadian designer that does a lot of custom-fitting work--despite the fact that she thinks in metric she drafts her patterns in inches because a millimeter is just too absurd of a level of precision. In class we talk about 1/16" being within the tolerance of your scissors or needle (especially in a coarse-weave fabric). 1 mm is SMALLER than 1/16"! 

    In science people work in metric and orders of magnitude; you might say that it is possible to precisely  measure a matchstick in mm, a piano in cm, and the distance to Paris in km. However it is nonsensical to measure a matchstick in km; every matchstick is approximately 0 km long. Likewise, you could go crazy trying to measure a piece of household furniture, or a human body, or a garment in mm, getting a different measurement every time with a standard lengthmeter like a dressmaker's measuring tape. I understand your point about easy math, but is anyone going to make me a clear gridded ruler with lines every mm? That is a ludicrous amount of precision, and would come out looking unusefully solid.

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  6. I'm Dutch but went to school in England before  they went metric so I am pretty comfortable with both systems. I have also worked for a German garment company in the Philippines where they use imperial and found the amount of work put into converting German specs(in metric) to imperial specs such a waste of time! As they used calculators and later computers to do the conversion, they would end up with inches with trailing decimals which would then again have to be converted to the nearest usable fraction of an inch on a tape measure! Needless to say this took a lot of time as well as lead to so many mistakes.Eleanor has a point that expecting a precision of 1mm is ludicrous, but on the other hand 1/16 is not much better! However in my experience, garment measurements are rarely specified down to that level of preciseness regardless of whether we are talking about inches or cm. Metric has my vote any time!

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  7. I'm Swedish so I have to say the metric system wins every time!! :) The Americans are just being stubborn using inches. *s* it's a pain.

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  8. Love the metric system. I find it much more regular, precise than imperial. You have another vote! I don't think cutting mats go down to mm ;)

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  9. The authors point was not a comparison of mm to inches. It was a comparison of metric to imperial. Your points about measurement resolution are somewhat redundant, if you don't need to be accurate to 1mm increments (I agree with you that this is an unnecessary level of precision) or don't have the ability to measure at that accuracy, (again agree that a tape measure really isn't THAT capable), then you just change your level of measurement resolution or your units to something more appropriate. Use 2mm increments or 5mm or 1cm. What makes the 1/16'' increments the standard? One could also argue that 1/16" is too finite a resolution.

    I agree with author in that it is FAR easier to perform calcuations in metric than it is imperial. You still round your calculations, but instead of having to determine the closest fraction approximation, you round to the appropriate decimal point/integer. This is simpler arithmetic & less prone to error.

    Finally, your point about rulers. Here is a site showing metric grading rulers;

    http://www.mrecht.com.au/Products/pages/Design/1.6_Rulers.htm

    You will find they use 2mm & 5mm increments.

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  10.  I'm an engineer in my 'outside of sewing' life & because I live outside of the US, I was brought up with the metric system.

    Every now & then, at university, we would get a lecturer that was particularly passionate about the metric system. He would demonstrate his passion by deliberating giving you exam questions or tutorial questions in imperial units. But that wouldn't be enough, he'd give you the measurements in units covering a range of magnitudes. For instance you'd get a pressure value in psi & a dimension in feet & ask you to calculate the force applied. Given that many of our exam questions involved many measurements or data inpoints, in a variety of units, it meant that we spent the first 10mins just converting all the formula inputs into units that could easily be combined before actually starting work on the question. With the metric system we would have simply moved the decimal points back & forth (multiplying or dividing by 10 a few times) to convert the units.

    It didn't take long for us to become equally passionate about the metric system.

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  11. When I first started learning some patternmaking, I memorized many fractions in decimal to the 3rd. That way the subtractions can be done more easily, just as you do with metric. I've also taken time to learn metric. I don't think it's that hard to learn both and remember both, but then I'm spatial with numbers so both systems make sense to me.

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  12. It baffles me too! Annoyingly I started sewing in UK with many american and UK based books as guides meaning I got used to imperial. Now I always use both but would rather stick to metric. 

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  13. Even as a kid, I realized that the metric system made more sense.  I'm American, and am totally comfortable with imperial, but it does take time to think through.  12 inches to a foot, 3 feet to a yard, 100 yards in a football field... And you'd be amazed at how many people don't know this stuff. 

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  14. We have been metric here in Australia since the 1960's.  Not sure why the US won't change. 
    Everything is metric - weights, temperature, distance etc.  So much easier.

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  15. you know how much my moulage changed my sewing...can't wait to see how you utilize yours!

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  16. Marina, great post. It generated so many interesting comments :) I was born and raised in the metric world. The first time I had to deal with imperial system was when I started sewing and reading American books and blogs. In more than 2 years of dealing with inches, I only remember that 5/8 inches = 1.5cm :)

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  17. I know this is an old post but a comment. It's not that bad to convert an arbitrary fraction to 16th of an inch or whatever the smallest gradation of your ruler is. Multiply the fractional part by 16 and you have your fraction expressed as 16ths. In your case 16*(1/6) = (2 2/3) 16ths of an inch. Which can be approximated well as 3/16. or can be plotted on the ruler more precisely, two-thirds of the way between 2 16ths and 3 16ths. Using a ruler graded in eighths multiply by 8. 8*(1/6)= (1 1/3) 8ths so plot 1/3 of the way past 1/8th or simply call it 1/8. Following through your calculation the back neck could be approximated numerically as 2 11/16" or more crudely as 2 5/8" but in either case plotted quite accurately just as you would do on a metric ruler. The trick is using the ruler correctly and it's not so much a relic of metric versus imperial units as how the ruler is graded. If you prefer using a calculator, there are inch rulers with gradations in tenths of an inch. In which case you could immediately plot whatever the calculator spits out.

    However, tailoring seems well suited to gradations in 16ths instead of 10ths. I know the neck is an annoying case where you break into sixths and there are also times when a fifth or a third is called for but far and away most the time you are splitting a measurement in half or in quarters, right? The beauty of this is a tailor could do those in their head and plot them exactly at a ruler gradations marked in 16ths. It's only the rare case when one has to break stride and remember what a sixth of an inch means. It's similar to music, no one will ever convert all musical notation to decimal measures. The natural thing to do while playing or composing is to break something in half and then in half again. The ear can't hear when an interval has been broken at 3/10th it will assume it heard 1/4. Yet 3/10th is easy to plot on a decimal ruler while 1/4 is between marks. In clothing fractions occur either because of the symmetries of the body or because, similar to music, the eye can spot proportions and finds them pleasing.

    The book Dress Pattern Designing by Natalie Bray was written around the time of the British changeover to metric and has an interesting discussion in the intro about how this should be applied to pattern drafting (intro is available in the amazon preview for anyone interested). She embraces designing in metric but does not believe an existing imperial drafting method should be simply converted to metric measurement by measurement. Instead it should be re-examined and when possible 1/2" should be converted as 1cm so that the new system is just as convenient to use as what it replace. You'll note that the real mistake made in your neck calculation was with the conversion, not the ruler. If you're working in metric, you shouldn't have to deal with things like 1.2cm which are simply a relic of the imperial draft. Bray also has a nice discussion of why measurements smaller than .5 cm are of no meaning in fashion drafting. Anyway, after going on so long, my suggestion would be if you do prefer metric, find a drafting system, such as Bray's, which has been engineered for metric. You'll then be able to enjoy something more intuitive and avoid inches at the same time.

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