HP 39gs Master Manual page 258

Another example of an existing aplet is shown right. It is called
"Tangent Lines" and it draws a tangent line onto a graph and then lets
the user move it around, displaying the gradient as it does so.
This aplet has the Function aplet as its parent because of the need to
graph functions. It has also had its menu adapted (see next
VIEWS
page) to show the options listed right. In this case the menu has far
fewer options because the operation of the aplet is very simple. The
reason for the "Start" option is discussed on page 261.
On the right is the menu for an aplet called "Curve Areas"
VIEWS
which finds the areas under curves using various approximations and is
used to introduce the definite integral. Because it deals with functions
and graphs its parent is the Function aplet. Some of the 'helper'
programs for this aplet are shown below. As you can see, their names
follow the naming convention discussed earlier.
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