How to Use Manual-Fit on Regression Lines on the TI-84 Plus

Do you think you could come up with a better line of best fit than your TI-84 Plus calculator did with its regression line? Go ahead and try! Manual Linear Fit enables you to visually find a line of best fit of the form Y=mX+b. Here are the steps for using Manual Linear Fit:

  1. Press [Y=] and deselect any functions that would graph by pressing [ENTER] on the corresponding equal sign.

  2. To open the Manual-Fit Wizard, press

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    Manual-Fit is located near the bottom of the Stat CALC menu. On the TI-84 Plus, it is the last entry in this menu.

  3. With your cursor on Store EQ, press [ALPHA][TRACE] to access the shortcut Y-VAR menu.

    See the first screen. Enter the number of the Y-VAR you want. Press the down arrow to Highlight CALCULATE and press [ENTER].

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  4. Use the arrow keys to navigate your cursor near the data point closest to the right part of the screen and press [ENTER].

    Two points determine a line; this establishes a point on the Manual-Fit line. As you move your cursor, the Manual-Fit line behaves like a moveable line as shown in the second screen.

  5. Use the arrow keys to navigate your cursor near the data point closest to the left part of the screen and press [ENTER].

    The Manual-Fit line is now drawn with the equation shown in the border at the top of the graph screen.

    The TI-84 Plus C displays functions and information in the border of the graph screen. The TI-84 Plus displays similar information directly on the graph screen.

  6. Use the left- and right-arrow keys to toggle the highlighted parameter values from m to b in the Manual-Fit line equation of the form, Y=mX+b.

  7. Enter a value for the highlighted parameter value to adjust the fit of your line.

    Notice, an entry line opens at the bottom of the screen as you enter a value for one of the parameters. See the third screen. Press [ENTER] to change the parameter in the equation and watch the graph automatically adjust.

  8. Press [GRAPH] to activate the on-screen prompt, DONE and then press [2nd][MODE] to exit the graph screen.

    This action stores the function and brings your cursor to the Home screen. On the TI-84 Plus, press [2nd][MODE] to store the function.

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