# Screentest

**URL:** <https://psychtoolbox.discourse.group/t/screentest/1352>\
**Category:** Uncategorized\
**Created:** [June 2, 2005, 4:55pm UTC](https://psychtoolbox.discourse.group/t/screentest/1352 "2005-06-02T16:55:03Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Allen\_Ingling](https://avatars.discourse-cdn.com/v4/letter/a/a183cd/32.png) [@Allen\_Ingling](https://psychtoolbox.discourse.group/u/Allen_Ingling)\
**Post date:** [June 2, 2005, 4:55pm UTC](https://psychtoolbox.discourse.group/t/screentest/1352/1 "2005-06-02T16:55:03Z")

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Hi  
  
I downloaded the latest release of PTB [Psychtoolbox OS X C Source Release 1.0.5 (11 April   
2005)], and do not find Screentest.m in the unpacked toolbox.  
  
I was wondering if this had been phased out, for some other testing program.  
  
Much thanks  
  
Lu Lesmes  
Salk Institute

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**Author:** ![mariokleiner](https://avatars.discourse-cdn.com/v4/letter/m/13edae/32.png) [@mariokleiner](https://psychtoolbox.discourse.group/u/mariokleiner)\
**Post date:** [February 6, 2013, 5:36pm UTC](https://psychtoolbox.discourse.group/t/screentest/1352/2 "2013-02-06T17:36:28Z")

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--- In [psychtoolbox@yahoogroups.com](mailto:psychtoolbox@yahoogroups.com), "sosy" wrote:  

> \>  
> \> Hi.I'm new in psychtoolbox.I'm using window 7 ,32 bits and matlab 2011 and installed psychtoolbox 3 ..and make a screentest..however,the output is questionable..below is the result :  
> \>   
> \> \>\> ScreenTest  
> \>   
> \> \*\*\*\*\* ScreenTest: Testing Screen 0 \*\*\*\*\*  
> \>   
> \>   
> \> PTB-INFO: This is Psychtoolbox-3 for Microsoft Windows, under Matlab (Version 3.0.10 - Build date: Oct 27 2012).  
> \> PTB-INFO: Type 'PsychtoolboxVersion' for more detailed version information.  
> \> PTB-INFO: Most parts of the Psychtoolbox distribution are licensed to you under terms of the MIT License, with  
> \> PTB-INFO: some restrictions. See file 'License.txt' in the Psychtoolbox root folder for the exact licensing conditions.  
> \>   
> \> PTB-INFO: Will disable DWM because a regular fullscreen onscreen window is opened -\> We want best timing and performance.  
> \> PTB-INFO: The detected endline of the vertical blank interval is equal or lower than the startline. This indicates  
> \> PTB-INFO: that i couldn't detect the duration of the vertical blank interval and won't be able to correct timestamps  
> \> PTB-INFO: for it. This will introduce a very small and constant offset (typically \<\< 1 msec). Read 'help BeampositionQueries'  
> \> PTB-INFO: for how to correct this, should you really require that last few microseconds of precision.  
> \> PTB-INFO: Btw. this can also mean that your systems beamposition queries are slightly broken. It may help timing precision to  
> \> PTB-INFO: enable the beamposition workaround, as explained in 'help ConserveVRAM', section 'kPsychUseBeampositionQueryWorkaround'.  
> \>   
> \>   
> \> PTB-INFO: OpenGL-Renderer is NVIDIA Corporation :: GeForce 9100M G/PCI/SSE2/3DNOW! :: 2.1.2  
> \> PTB-INFO: VBL startline = 768 , VBL Endline = 768  
> \> PTB-INFO: Measured monitor refresh interval from beamposition = 17.008407 ms [58.794455 Hz].  
> \> PTB-INFO: Will use beamposition query for accurate Flip time stamping.  
> \> PTB-INFO: Measured monitor refresh interval from VBLsync = 16.660104 ms [60.023634 Hz]. (288 valid samples taken, stddev=0.351685 ms.)  
> \> PTB-INFO: Reported monitor refresh interval from operating system = 16.666667 ms [60.000000 Hz].  
> \> PTB-INFO: Small deviations between reported values are normal and no reason to worry.  
> \> PTB-INFO: Support for fast OffscreenWindows enabled.  
> \>   
> \> \*\*\*\*\* ScreenTest: Done With Screen 0 \*\*\*\*\*  
> \>   
> \> Questions : 1. Is the result saying that psychtoolbox will not working well?  
> \>   
> \> 2.Do i need to install back the toolbox?  
> \>   
> \> Need your advice.Thank you  
> \>

It says:  
  
PTB-INFO: for it. This will introduce a very small and constant offset  
(typically \<\< 1 msec). Read 'help BeampositionQueries'  
PTB-INFO: for how to correct this, should you really require that last few microseconds of precision.  
  
If you don't care about stimulus onset timestamps which are up to 1 msec off, then it's likely fine. You can always run VBLSyncTest and PerceptualVBLSyncTest for some more checks.  
  
The only thing i see is that system timing seems to be quite a bit noisy, but sometimes that's an outlier and then you use Windows-7 which is famous for noisy timing, so often expected.  
  
-mario