SI Units, Imperial Units, and why the two don't mix?

Discussion in 'AutoCAD' started by hutch, Apr 6, 2004.

  1. hutch

    hutch Guest

    Could someone point me to information that would help fuel a discussion on english, and metric conversion and accuracy problems when converting back and forth in a programming environment?
    I have a situation where this is done in the user interface and internally within the code. Problems are apparent and I need some ammo!
     
    hutch, Apr 6, 2004
    #1
  2. hutch

    Ian A. White Guest

    The accuracy problem generally results when you use fractional rounding
    in imperial units. 1/16" is 1.5875 mm, so if you want the metric
    dimension and the imperial one to match to within 0.1 mm, you will need
    the imperial fractional rounding to be 1/256" (to the nearest standard
    imperial fractional increment). Of course if you had an imperial drawing
    done with every dimension accurate to 1/256", it would give everyone a
    bit of a laugh.

    When a drawing has dual dimensions and those using the drawing can use
    either set of values, then both have to have the same level of accuracy.
    This is why the primary units take precedence over the alternate units.
    The alternate units are for information only. The primary units always
    apply.

    So if you convert between either, you have to use the same accuracy.
    With metric dimensions you can go to 2 or 3 decimal places relatively
    easily. With fractional imperial units it becomes a little silly, this
    is why when it comes to machining drawings in imperial units the revert
    to decimal imperial for that very reason.
     
    Ian A. White, Apr 7, 2004
    #2
  3. Hm... we work to 1/256" for all dimensions all the time, and it doesn't cause
    problems unless someone screws up.

    But then again, we're Architects.

    Matt

     
    Matt Stachoni, Apr 7, 2004
    #3
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