Vernier Graphical Analysis 3 User Manual
Page 24
Graphical Analysis for Windows TEACHER’S MANUAL
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These are fairly standard formulas.
The coefficient of regression is a useful measure of how well the data fit a straight
line, but it should not be overused. Always examine the graph. The coefficient is greatly affected by a few extreme
points.
Smoothing
When Smooth Ave is used in a calculated column, the column data, z
j
, is a weighted average of the number of points
selected by the user to use in smoothing, m. DerivativeSG("Y", "X") returns the Savitsky-Golay derivative of "Y" with
respect to "X". A polynomial is fitted to N points around each point and the derivative of that polynomial is used. N may
be set in File:Settings. This is very accurate but can be slower than other methods. For more information about Savitsky-
Golay methods see Numerical Recipes in C http://lib-www.lanl.gov/numerical/bookcpdf.html chapter 15.
z
w y
w
j
i
j
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n
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n
i
i
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=
⋅
−
=−
=+
=−
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∑
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(
)
[ ]
(
)
w
m
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= ∗
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Modifying Graphical Analysis
If you do not want your students to use certain features of this program, we have provided a method for disabling menu
items or toolbar items. You might use this feature to disable the Automatic Curve Fit option, so that students are
required to use Manual Curve Fit to find a fit. To do so, call up Preferences from the File menu. Uncheck the box next
to Allow Automatic Curve Fit. When you are finished editing the file, save it. From there, you can have that file get
called up whenever Graphical Analysis is launched or New is selected from the File menu. Use the Browse button to
locate your Startup File.
3
Refer to a statistics text for more information; for example, An Introduction to Error Analysis by John R. Taylor,
Oxford University Press, 1982.