Beginning to understand the relationship between change and accumulation is a precursor to understanding calculus. This example illustrates the use of dynamic graphs to learn about change and linear relationships, as described in the Algebra Standard.
The following links to an updated version of the eexample.

Cost per Minute (6.2)
Explore a linear function or a piecewise function comparing units
vs. cost per unit in order to find the total cost of a phone plan.

The eexample below contains the original applet which conforms more closely to the pointers in the book.
In
this twopart example, users can drag a slider on an interactive
graph to modify a rate of change (cost per minute for phone use)
and learn how modifications in that rate affect the linear graph
displaying accumulation (the total cost of calls).

Constant Cost per Minute (6.2.1)
The cost per minute for phone use
remains constant over time


Changing Cost per
Minute (6.2.2)
The cost per minute for phone use changes after the first sixty minutes of call..
