Vernier Original LabQuest - Manual (Page 17)

LabQuest Reference
15
Curve Fit
Curve Fit allows you to automatically fit a chosen
function to your data. If a region of the graph is
selected, only that region is used for fitting. If there is
no selection, the entire width of the graph is used.
Choose the desired fit equation from Proportional,
Linear, Quadratic, Power, and Natural Exponent. On
choosing the fit equation, LabQuest will perform the fit
and display the coefficients and Root Mean Square
Error (RMSE). Tap OK to return to the main Graph
screen. Choose Curve Fit again to remove the fit.
Tip: The RMSE (root mean square error) is a measure of how well the fit matches the data.
The smaller the RMSE, the close the data are to the fitted line. The RMSE has the same
units as the y-axis data.
Once you have a fit on the main graph, you can choose Interpolate from the Analyze menu.
Tap on the graph to read values from the fitted curve (as opposed to reading from the data)
as a function of the x-axis value. Turn off Interpolate
by selecting it again.
Model
Model allows you to manually fit a chosen function to
your data. Choose Model, and then choose a function.
The parameters A, B and C are adjustable. Change them
by direct entry or by using the up and down arrows to
the right of the values. Tap OK to place the model on
your main graph.
Tip: If no function appears when modeling, your parameters are defining a curve that is
outside of the plot window.
Draw Prediction
The Draw Prediction choice gives you a free-hand
sketch tool superimposed over a graph. This can be
used for a variety of purposes, but most often is used to
sketch a prediction of how a graph will appear once
data are subsequently collected. Choose Draw
Prediction, and then Graph 1 or 2 as desired. You will
then see a sketching screen. Drag the stylus across the
screen for smooth curves, or tap the screen to connect
the taps with straight-line segments. The Reset button
will remove your sketch if you need to start over. Tap OK to place your sketch on the main
graph. To remove a prediction, choose Draw Prediction again from the Analyze menu.