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AutoCAD® 2012 FOR DUMMIES® by David Byrnes

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Controlling Your Precision

In AutoCAD, lack of precision makes later editing, hatching, and dimensioning tasks much more difficult and time consuming. Keep these facts in mind:

  • Small errors in precision in the early stages of creating or editing a drawing often have a big effect on productivity and precision later.
  • Drawings may guide manufacturing and construction projects; drawing data may drive automatic manufacturing machinery. Huge amounts of money and even lives can ride on a drawing's precision.

In recognition of these facts, a passion for precision permeates the profession. Precision is one of the characteristics that separates CAD from ordinary illustration-type drawing work. The sooner you get fussy about precision in AutoCAD, the happier everyone is.

CAD precision versus accuracy

You often hear the words precision and accuracy used interchangeably, but it's useful to understand the difference. In this book, I use precision to mean controlling the placement of objects so they lie exactly where you want them to lie in the drawing. For example, lines whose endpoints meet must meet exactly, and a circle that's supposed to be centered on the coordinates 0,0 must be drawn with its center exactly at 0,0. I use accuracy to refer to the degree to which your drawing matches its real-world counterpart. An accurate floor plan is one in which the dimensions of the CAD objects equal the dimensions of the as-built house. In a sense, then, it's not the drawing that should be accurate ...

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