Logger Pro

To change the number of points in the derivative calculation, open the File menu and choose Settings For FILENAME. Then adjust the number of points for derivative calculations and select OK.

LabQuest

To change the number of points in the derivative calculation, open the File menu and choose Settings. Then adjust the number of points for derivative calculations and select OK.

Graphical Analysis and Vernier Video Analysis

To change the number of points in the derivative calculation, open the Other Options menu (three dots at the top right of the app window) and choose Session Preferences. Then adjust the number of points for derivative calculations and click or tap the X to exit the Session Preferences dialog.

When and why would you do this?

Logger Pro, Graphical Analysis, Vernier Video Analysis, and LabQuest App use a derivative function for some tasks, including calculating velocity and acceleration from position data. See How do Logger Pro, Graphical Analysis, LabQuest app, and Vernier Video Analysis calculate velocity and acceleration?

Across all of our software that performs derivative calculations, the default number of points for the derivative calculation is 7 (the central point and 3 points to either side).

There are a few cases when one might wish to adjust the number of points used in a derivative calculation. Using a greater number of points results in a smoother derivative graph, but the effect of changes in the source data is smeared in time. On the other hand, using fewer points for the derivative calculation results in a more responsive graph with more noise.

For example, in an experiment where a person is walking in front of the motion detector, using 15 points for derivatives will result in quieter, more easily interpreted velocity graphs. The temporal averaging will not affect interpretation.

On the other hand, in a mass-on-a-spring simple harmonic motion experiment, using more than 5 or so points may result in excessive averaging, altering the magnitude of the peak velocity and acceleration values. Another case in which you might want to reduce the number of points in a derivative calculation is when you have fewer data points in the source column.

It is easy to observe the effect of changing the number of points used in derivatives, as the setting takes effect immediately, acting on existing data. One can optimize the setting as needed.

Once the number of points used for the derivative calculation has been changed for a given file, that change sticks with the file. If you save the file, the next time you open the file you will find that the change made will have stuck with that file, and it will not automatically go back to 7 points.

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