ALERT: SEWING GEEK-OUT FOLLOWS....... Proceed with caution and patience...
Sometimes you understand a concept and sometimes you really get it. Since I learned about precision and accuracy in elementary school science, until the past few weeks, I have merely understood the concepts of and difference between precision and accuracy. Now that I've had some time working with flat patternmaking and draping I feel that I really get it.
Wikipedia has a great entry with visuals on precision and accuracy, so there's no use paraphrasing. Here's just one real-life example:
I traced around my sloper, rotated darts, added ease, etc., then traced around that pattern onto paper I would pin down to cut the fabric. Well, if I added even 1/16" around the sloper the first time I traced, then added another 1/16" around the modified pattern to the usable pattern, I added 1/8" total size all around over the sloper. Doesn't sound like much, but if you do this (*ahem*, does it sound like I have personal experience with this?) on a fitted princess seam bodice with a back zip, that totals 14 seam allowances for a total increase of 7/8" around the width of the bodice. My work was precise on each pattern piece, but the end result was very inaccurate when you compared the sewn-up sloper to the sewn-up newest pattern.
Conversely: one insomniac night, I draped a top on Clementine for the most accurate fit and compared the pieces to the flat pattern. Not even close in some areas. How bizarre and non-intuitive, right? Very accurate fit, but completely imprecise compared to the flat pattern.
For those of you who have seen The Fashion Show -- I think in episode 3, when Reco was team leader, he drew a pattern piece freehand, just eyeballing it on the paper. I know the resulting garment was spot-on, and I'd bet his results were both accurate and precise. I bet that mastery takes years and years and maybe even a special gift.
Precision vs. accuracy. Flat pattern vs. draping. I see this is what my sewing guru meant when she said that many patterns are best designed using both. (BTW, if you've read this far, I'm by no means implying that draping can't be precise. I guess I'm just not a precise draper yet.)