using_units

By default, Mathcad uses units from the SI unit system (International System of Units). Mathcad offers several choices of unit systems: SI, CGS, MKS, U.S. customary units, or no unit system.

One of the handy features of Mathcad is its ability to track standard units during calculations and to convert the units of calculated quantities automatically. For example, you can define a variable in terms of the built-in unit kilometers simply by multiplying a number by

. Here we define the radius of the earth and a surface area function:

(The symbol

is also available on both the Calculator toolbar and the Greek Symbol toolbar.)

Then you can evaluate these expressions directly, or perform more extensive calculations involving them:

Notice that the result is automatically shown in terms of the base units of your default unit system — in this case SI.

To see what the surface area of earth equals in hectares, click once on any part of the equation below and notice the trailing black box on the right-hand side. Double-click on this black box to bring up the Insert Unit dialog box. Then double-click on one of the displayed units to replace the units shown.

This principle holds for all of the Mathcad built-in units, which is a very extensive list, as well as for any units you may wish to define yourself. To see the list of built-in units in Mathcad, choose Unit from the Insert menu.

The units feature is also very convenient because it lets you know if you have made a mistake in the units in your calculations. For example, the force calculation below should end up in newtons (or an equivalent force unit) . . .

. . . but it appears to have an extraneous factor of

. Looking closely at the statements in the calculation, you can see that the definition of the acceleration

is missing a term of

To display units in fractional form choose Result under the Format menu. Under the heading “Unit Display,” check “Format Units” and “Simplify Units when possible.” Units in your results will display as shown below. These options can be set as the default or for individual equations.

Now find out about accessing the Mathcad Collaboratory on the Web.