# Error of the grating size

**URL:** <https://discourse.psychopy.org/t/error-of-the-grating-size/43031>\
**Category:** Builder\
**Created:** [November 22, 2024, 3:56am UTC](https://discourse.psychopy.org/t/error-of-the-grating-size/43031 "2024-11-22T03:56:21Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![C\_jojoy](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/c_jojoy/32/43403_2.png) [@C\_jojoy](https://discourse.psychopy.org/u/C_jojoy)\
**Post date:** [November 22, 2024, 3:56am UTC](https://discourse.psychopy.org/t/error-of-the-grating-size/43031/1 "2024-11-22T03:56:22Z")

</div>

OS (e.g. Win10): Win 11  
PsychoPy version (e.g. 1.84.x): 2024.2.4  
Standard Standalone? (y/n) If not then what?:  
What are you trying to achieve?: Display the grating stimulation in full screen using deg units  
What did you try to make it work?: Use anothe units “degFlat”  
What specifically went wrong when you tried that?:  
It’s something that’s been bothering me for a long time.  
I want to use deg units to build a full-screen grating stimulus on my monitor, but when I set the size in the grating properties, the grating image I get doesn’t match the size calculated using trigonometry!  
My monitor info:  
Resolution: 2560 x 1440pixels  
Width: 61.13cm  
Distance from screen: 30.565cm  
If I want the image to spread over the full screen, the calculated w of size=2\*arctan(30.565/61.13/2)=90°, right?  
But when I set the size’s w to 90°, I get a grating image that is very small, I don’t know what’s wrong, can anyone help me? Thank you very much!  
There are some picture of experimental setting:

 ![0843eea081aeb99a53106ad1ce401dbb_720](https://us1.discourse-cdn.com/flex002/uploads/psychopy/original/3X/9/0/9055368aa6dcf83a4b1cd0acf950c364e6f2165e.png)  
 ![2](https://us1.discourse-cdn.com/flex002/uploads/psychopy/original/3X/c/e/ce357f25064bdf593e48262cb537d458522e6b7e.png)