# The difference between the real size and the size calculated using 'deg' units of grating stimulation

**URL:** <https://discourse.psychopy.org/t/the-difference-between-the-real-size-and-the-size-calculated-using-deg-units-of-grating-stimulation/43011>\
**Category:** Builder\
**Created:** [November 21, 2024, 1:24pm UTC](https://discourse.psychopy.org/t/the-difference-between-the-real-size-and-the-size-calculated-using-deg-units-of-grating-stimulation/43011 "2024-11-21T13:24:13Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Starrr](https://avatars.discourse-cdn.com/v4/letter/s/b782af/32.png) [@Starrr](https://discourse.psychopy.org/u/Starrr)\
**Post date:** [November 21, 2024, 1:24pm UTC](https://discourse.psychopy.org/t/the-difference-between-the-real-size-and-the-size-calculated-using-deg-units-of-grating-stimulation/43011/1 "2024-11-21T13:24:13Z")

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I

**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:

 ![3](https://us1.discourse-cdn.com/flex002/uploads/psychopy/original/3X/b/7/b7546ac7d3c1657aa9bbbe95adf41880de03bfd7.png)  
 ![2](https://us1.discourse-cdn.com/flex002/uploads/psychopy/original/3X/c/e/ce357f25064bdf593e48262cb537d458522e6b7e.png)