Units and Computer Algebra Systems

With a little cleverness you can use your computer algebra system to keep track of units. We will illustrate how this can be done using the TI-92. If you have a TI-92 you should follow along using it. You can also follow along using Maple or Mathematica by clicking on the appropriate button at the right.. The TI-92 button is inactive because this file already has TI-92 instructions.

Maple Mathematica TI-92

Begin by choosing one basic unit for each kind of measurement -- for example, we will choose feet as our basic unit for length and seconds as our basic unit for time. We will use the corresponding variables -- feet and seconds -- in our computer algebra system. If you have used either of these variables then you will have to "clear" or "undefine" it. To clear a variable in the TI-92 go to the VAR-LINK menu, select the variable to be cleared as shown in the screen at the right
and then press F1 to see the screen at the right.
Notice that Delete is highlighted in the pull-down menu. Press ENTER. A dialog box will appear to confirm that you want to delete the variable.
Press ENTER to delete the variable that you selected earlier. Notice that this variable disappears from the list of variables.
Now you can do simple calculations involving these basic units as shows in the screen at the right.
You can define additional units in terms of these basic units as shown in the screen at the right.
Now your computer algebra system will do conversions automatically as shown in the screen at the right.

The TI-92 will display all your results in terms of the basic units you chose. You should choose your basic units with this in mind -- for example, if you want results displayed in miles per hour then choose miles as your basic unit for length and hours as your basic unit for time.