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2412 Views 6 Replies Latest reply: May 16, 2008 12:00 AM by TomGutman RSS
davida Copper 3 posts since
Oct 24, 2006
Currently Being Moderated

May 14, 2008 12:00 AM

MathCad 14 units

Need some help with defining units in mathcad 14.


I define a diameter and assign (in) as the unit. Then I re-enter the variable and the unit changes to ft. How can I stabilize the units so they come out the same way every time I use them?
  • StuartBruff Platinum 4,731 posts since
    Jun 1, 2007
    Currently Being Moderated
    May 14, 2008 12:00 AM (in response to davida)
    MathCad 14 units
    On 5/14/2008 4:31:10 PM, davida wrote:
    == I define a diameter and assign (in) as the unit. Then I re-enter the variable and the unit changes to ft. How can I stabilize the units so they come out the same way every time I use them?

    If you mean have the units display as you input them every time regardless of what the default unit is, then you can't. All you can do is enter the appropriate unit in the placeholder.

    If you mean that you would like to set the default unit to in rather than ft, then
    a. from the menu select Tools\Worksheet Options,
    b. then the 'Unit System' dialog,
    c. select 'Custom' in the 'Default Units' button group
    d. click 'Length' in the 'Base Dimensions' listbox
    e. click the adjacent 'Change' button
    f. select your desired unit from the 'unit' listbox
    g. start clicking 'OK' buttons until you're back at the worksheet!

    Stuart
  • TomGutman Silver 10,537 posts since
    Oct 22, 2006
    Currently Being Moderated
    May 14, 2008 12:00 AM (in response to davida)
    MathCad 14 units
    Mathcad (any version) does not actually do units, except for input and output. When you enter a length in inches, you are not assigning inches as the unit. Rather you are expressing the length in inches and Mathcad will convert the specified length to it's internal representation for that length. In principle a user would not need to know what that internal representation is. In MC14 it will be meters, no matter what unit system is chosen and no matter what unit was used to enter it.

    You can choose the default unit to be used by Mathcad when displaying a value (such as a length) by choosing a unit system. With a custom system you can choose the particular unit for any standard type of quantity, you are not restricted to seeing the "standard" unit for any particular system. And you can always choose specific units (whether or not standard -- pi is often a useful unit) for any specific display by using the units placeholder.
    __________________
    � � � � Tom Gutman
    • PhilipOakley Silver 2,084 posts since
      Feb 20, 2007
      Currently Being Moderated
      May 16, 2008 12:00 AM (in response to TomGutman)
      MathCad 14 units
      On 5/14/2008 5:16:59 PM, Tom_Gutman wrote:
      And you
      >can always choose specific
      >units (whether or not standard
      >-- pi is often a useful unit)
      >for any specific display by
      >using the units placeholder.
      >__________________
      >� � � � Tom Gutman

      For the pedants. (and Tom already knows this anyway;-)

      You may have though pi as unitless, becaue it isn't in kg or metres but is 'just' a number.

      The pedant notes that metres are of dimension 'Lenght'and kg are of dimension 'mass'.

      To report a value one must scale it to be 'counted' using the local customary measure for that dimension, a scaling factor. The particular 'scaling factor' that resuklts in teh answwer 1, that is 'unity' is obviousl the "Unit".

      So commonly we may want to know, relative to pi, how many of the thing we have. Hence puting pi inti the results place holder does that scaling.

      We can also have, say, Tonne, relative to a mass dimension (internally in kg) doing the autoscaling factor, to give answers countes in those very same Tonnes.

      Thus we have the pedants disctinction between "Units" and "Dimesions". But we know everyone just puts all these concepts into the same "Units & Dimensions" bag and gives them a good shake ;-)

      There is much more of this for the true pedant. but that is enough for (k)now.

      Philip Oakley
  • PhilipOakley Silver 2,084 posts since
    Feb 20, 2007
    Currently Being Moderated
    May 16, 2008 12:00 AM (in response to StuartBruff)
    MathCad 14 units
    On 5/16/2008 6:25:40 AM, stuartafbruff wrote:
    >A true pedant would shoot whoever wrote
    >your spell-checker :-)
    >
    >Stuart

    That would be Mr Darwin, Beagle school of sailing, class 1c.

    Philip Oakley
  • StuartBruff Platinum 4,731 posts since
    Jun 1, 2007
    Currently Being Moderated
    May 16, 2008 12:00 AM (in response to PhilipOakley)
    MathCad 14 units
    On 5/16/2008 5:27:46 AM, philipoakley wrote:
    == The pedant notes that metres are of dimension 'Lenght'and kg are of dimension 'mass'.

    The pedant (I asked one) would have said the 'metre', symbol 'm', is the base measurement unit of the quantity 'length' within the SI, and has dimension 'L'.

    A true pedant would shoot whoever wrote your spell-checker :-)

    Stuart
    • TomGutman Silver 10,537 posts since
      Oct 22, 2006
      Currently Being Moderated
      May 16, 2008 12:00 AM (in response to StuartBruff)
      MathCad 14 units
      >>The pedant (I asked one) would have said the 'metre', symbol 'm', is the base measurement unit of the quantity 'length' within the SI, and has dimension 'L'.<<

      That would be in some theoretical, abstract, universe of discourse, perhaps a standards body. In Mathcad, m is just an ordinary symbol whose value is one meter (using whatever internal representation of one meter Mathcad chooses to use -- that is not consistent across all Mathcad environments and sheets). It's status as a unit, or base unit, is based on how it is used, not its intrinsic properties.
      __________________
      � � � � Tom Gutman

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