In this tutorial we will discuss two topics that fall under the heading of useful but not often used. The first topic discusses creating userdefined constants. The second topic discusses the need to occasionally adjusting the graph's scale.
Creating userdefined constants. As you know the builtin constant PI( ) is used when you wish to express the value of p. Excel also allows the user to define his or her own constants. For example, you will notice that many of the physics formulas you will encounter this year make use of many constants such as g, the acceleration due to gravity. At our latitude in Clemson, SC, we experience an acceleration due to earth's gravity which is g = 9.80 m/s^{2}. You will find that you will use the value for g throughout the year. When using Excel, rather than typing 9.80 each time you wish to express the acceleration due to earth's gravity, you can define the constant with a descriptive name or symbol, say in this case, 'g', to equal 9.80. Then simply use your defined constant, g, in your formulas. Let us work a nonphysics example to see how to define our own constants. Again, there are several ways to define constants, but this is one method that I think will be most helpful. Say, for example that you are the owner of a produce stand and you wish to use Excel to calculate the amount each customer owes. This amount is dependent on the cost of each produce item and also the quantity purchased. Say, you sell apples for $0.25, oranges for $0.45, and pears for $0.65. These costs change on a daily basis, so it will be helpful to be able to quickly and easily change the costs of the produce without having to change any of your total cost formulas. Your first step is to set up a data table like the one to the right. Notice that the words "Apples", "Oranges" and "Pears" appear next to their individual purchase cost. While this is not imperative, it is helpful to organize your table this way. Also notice the Name Box is encircled in the screen shot to the right. This indicates that cell B3 has been clicked on. You should also be aware that the formula bar indicates that the value for cell B3 is 0.25. There is nothing new here. Now we wish to define three constants that represent the cost of each produce item. Let us define our first constant as "apple" to represent the cost of an apple. To do this, follow the steps below:
If you would like to delete a constant, the easiest way is to click Insert >> Name >> Define on the Menu Bar. Then select the appropriate constant and click the Delete button. Adjusting the graph's scale. Often you will plot data that is relatively constant. For instance, say you measure the velocity of an air track glider on a level track. The velocity of the glider in this situation should be constant as the data to the right shows. However, when Excel plots the data, the scale of the velocity axis is such that the data appears to be widely varying as shown below.
To make the graph display a more obviously linear trend, we need to expand the scale of the vertical (velocity) axis. To do so, simply doubleclick on the vertical axis and change the scale accordingly. The final result is shown below:
Note that both graphs plot the same data! The only difference in the graphs is their scale.
Note that the axis maximum and minimum were
entered manually as indicated by the red circles in the above
screen shot.


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