On the control part of the graph select the Rb/Sr option.

Rember that the Half-life of Rb-87 is 48.8 Billion Years. Note that the scale on the horizontal axis is now 10 times greater than the vertical axis.

Click the "up" arrow and watch the slope of the isochron change over time.

You can also type numbers directly into the text box displaying the slope. Press the return key to activate any typed-in change.

Go ahead and complete the table.