# Cedrus Box Timing Output Issue

**URL:** <https://discourse.psychopy.org/t/cedrus-box-timing-output-issue/46934>\
**Category:** Builder\
**Tags:** timing, buttons, response\
**Created:** [April 7, 2026, 12:36pm UTC](https://discourse.psychopy.org/t/cedrus-box-timing-output-issue/46934 "2026-04-07T12:36:34Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Abbie\_Robinson](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/abbie_robinson/32/39333_2.png) [@Abbie\_Robinson](https://discourse.psychopy.org/u/Abbie_Robinson)\
**Post date:** [April 7, 2026, 12:36pm UTC](https://discourse.psychopy.org/t/cedrus-box-timing-output-issue/46934/1 "2026-04-07T12:36:34Z")

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**OS** : Win10  
**PsychoPy version** : 2026.1.2  
**Standard Standalone Installation?** yes  
**Do you want it to also run online?** no

**What are you trying to achieve?:** I am running a random dot motion task locally which uses a Cedrus RB-530 to collect directional responses to coherent dot motion going left or right. I have installed the Cedrus plug-in and button presses are being registered when the task is run. My issue is the output datafile. The start and stop times of the Cedrus box are correct and appearing in line with the stimulus. However, I am not sure how the actual reaction time is being recorded. When using a keyboard, I would be given a key\_resp.rt column showing the second a response was made. However, I am unsure of the values that are given in the dots\_resp.times column for the Cedrus box responses.

 ![image](https://us1.discourse-cdn.com/flex002/uploads/psychopy/original/3X/a/e/ae79c362a2d2d6ec502bd43ab5a0dc9f45b7e5ff.png)

**What did you try to make it work?:** I have checked the functionality of the Cedrus box using Xidon 2 and the timing of the box itself appears to be accurate.

I would please like advice on understanding this output or how to save a .rt style column for Cedrus presses in the datafile.

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**Author:** ![TParsons](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/tparsons/32/8301_2.png) [@TParsons](https://discourse.psychopy.org/u/TParsons)\
**Post date:** [April 9, 2026, 10:45am UTC](https://discourse.psychopy.org/t/cedrus-box-timing-output-issue/46934/2 "2026-04-09T10:45:54Z")

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In your Button Box Component, in the Data tab, do you have “Sync timing with screen refresh” ticked? If so, then the times stored will be relative to experiment start; so you can get the time since the Routine began by subtracting the value in the `<routine name>.started` column. Alternatively, if you uncheck that box, times will be relative to Routine start.

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**Author:** ![wakecarter](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/wakecarter/32/5753_2.png) [@wakecarter](https://discourse.psychopy.org/u/wakecarter)\
**Post date:** [April 9, 2026, 11:33am UTC](https://discourse.psychopy.org/t/cedrus-box-timing-output-issue/46934/3 "2026-04-09T11:33:57Z")

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So Button Box is different from keyboard where .rt is (I believe) relative to the start of the component?

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<div class="post-metadata">

**Author:** ![TParsons](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/tparsons/32/8301_2.png) [@TParsons](https://discourse.psychopy.org/u/TParsons)\
**Post date:** [April 9, 2026, 12:29pm UTC](https://discourse.psychopy.org/t/cedrus-box-timing-output-issue/46934/4 "2026-04-09T12:29:13Z")

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It’s more that `.rt` is different than `.times`, but as Button Box has `.times` and Keyboard has `.rt` that is essentially the case, yes. `.times` is “When was this button pressed”, `.rt` is “How long after this Component started was this button pressed” (essentially, `rt = times - started`)

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**Author:** ![Abbie\_Robinson](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/abbie_robinson/32/39333_2.png) [@Abbie\_Robinson](https://discourse.psychopy.org/u/Abbie_Robinson)\
**Post date:** [April 9, 2026, 4:55pm UTC](https://discourse.psychopy.org/t/cedrus-box-timing-output-issue/46934/5 "2026-04-09T16:55:22Z")

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Hi Todd, thanks for the response! “Sync timing with screen refresh” is ticked for the dots stims and resp components. Even with subtracting, the resultant time is too high. I ran a few trials and the datafile is below if needed. When subtracting, it leaves an impossible RT of 16.945148s, despite the routine only being 2s long. Would appreciate any advice on how to go about fixing this!

[833338\_RDK\_EEG\_Triggers\_V2026\_ButtonBox\_2026-04-09\_17h29.41.520.csv](https://discourse.psychopy.org/uploads/short-url/1qGI5yppMcOXx1h528CVEJEAuOw.csv) (5.6 KB)

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**Author:** ![stanley1O1](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@stanley1O1](https://discourse.psychopy.org/u/stanley1O1)\
**Post date:** [May 4, 2026, 7:32pm UTC](https://discourse.psychopy.org/t/cedrus-box-timing-output-issue/46934/6 "2026-05-04T19:32:26Z")

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> [@Abbie\_Robinson](#):
>
> Cedrus RB-530

If you don’t want to do the manual math to calculate the RTs you should remove the Cedrus button box plugin. I found that it is not necessary for basic use cases of collecting RT data. IIRC it’s an issue as to how the cedrus plugin times responses, it doesn’t like to use the timestamp relative to the trial, or object onset, but instead uses onset of the experiment always.

Remove the Cedrus plugin, then just use a basic keyboard component and the cedrus box works for that (you will need to change the manual switches on the box, to set it as letters or numbers as the output for you want).

As an aside, our lab has actually started to move away from Cedrus due to the lack of support and how much other hardware has caught up when it comes to sampling rates and button press registration customization. For a fraction of the cost.

Issac