This issue was fixed in Graphical Analysis 5.18.1. Users of this or newer versions will not have to do any of the steps below.

This article pertains to the now-obsolete release of Graphical Analysis and Graphical Analysis Pro v5.18.0-3098 on all platforms as well as the Progressive Web App version (

There is a bug in this version of Graphical Analysis when measuring linear motion (distance, velocity, and acceleration) in which the flag spacing reverts to 0.05 m and the number of flags reverts to 8 when different objects are chosen such as the Ultra Pulley or the Cart Picket Fence. This affects all experiments using the photogate including experiments using the original Centripetal Force Apparatus (CFA), but NOT including Picket Fence Free Fall using the Vernier Picket Fence (PF).

This bug is fixed in an update of Graphical Analysis. To check if there is an update available, click or tap on the three dots at the top right of the Graphical Analysis window and select Check for Updates.

You can also sign up to be notified when the update is released.


There are two workarounds for this problem.

Before data collection

Before data collection, in the photogate settings, change the object to Other / User Defined and enter the following:

Object Flag Spacing Number of Flags
Cart Picket Fence 0.01 13
Ultra Pulley – in groove 0.015 10
Ultra Pulley – outside edge 0.016 10
Bar Tape 0.016 any value*
*When using the bar tape, you can enter any number of flags. If you want to end data collection after a specific number of flags, that number must be entered in the Number of Flags field.

IMPORTANT: The first data set collected will look incorrect, as if the bug has affected this too. To correct the problem, open the Data Collection Settings again, note that your settings are still there (the number of flags has changed to 8, but that does not affect your measurements), and click or tap Done. Your subsequent data collection runs will be correct. If you like, delete Data Set 1. To do this, go to the data table and click or tap the three dots at the right end of the bar marked Data Set 1. Select Delete Data Set. When a window pops up toconfirm that you want to delete the data set, click or tap Delete.

After data collection

After data collection, in the data table, create a new distance calculated column to correct the distance values, and create a new velocity calculated column to correct the velocity values.

Click or tap the three dots in the heading of the distance column. Select Add Calculated Column.
To create a column for the correct distance values, follow these steps:

1. Enter a name and units for the calculated column.
2. Click or tap Insert Expression and select Custom Expression if you are using Graphical Analysis Pro.
3. Create the expression “Distance”*0.3 to convert from Vernier Picket Fence measurements (increments of 0.05 m) to Ultra Pulley in groove measurements (increments of 0.015) or use an appropriate factor for another object.

If you are not using Graphical Analysis Pro, choose the expression A*X^B and enter 0.3 for Parameter A (or the appropriate factor for your object), Distance for Column X, and 1 for Parameter B.

Click or tap Apply.

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To create a column for the correct velocity values, follow the steps similarly to creating the correct distance column, but use the expression 1st Derivative (Y,X). This image has an empty alt attribute; its file name is Screenshot-2023-09-07-at-12.38.11-PM-775x1024.png
Select your corrected distance column in the dropdown menu for Column Y, and select Time for Column X. Now you will have a corrected Velocity column.
Now you can graph the corrected velocity vs. time and determine the acceleration, if desired.

Click or tap on the vertical axis label of your graph to open the Plot Manager.

Then select the column you would like to graph.

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