6 Replies Latest reply: May 16, 2008 12:00 AM by TomGutman RSS

    MathCad 14 units

    davida Copper
      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?
        • MathCad 14 units
          StuartBruff Platinum
          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
          • MathCad 14 units
            TomGutman Silver
            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
              • MathCad 14 units
                PhilipOakley Gold
                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
              • MathCad 14 units
                PhilipOakley Gold
                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
                • MathCad 14 units
                  StuartBruff Platinum
                  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
                    • MathCad 14 units
                      TomGutman Silver
                      >>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