# I am recieving a value of 10 for the screen number when I only have 2 screens **URL:** \ **Category:** Programming Help\ **Created:** [December 12, 2025, 5:44pm UTC](https://psychtoolbox.discourse.group/t/i-am-recieving-a-value-of-10-for-the-screen-number-when-i-only-have-2-screens/5776 "2025-12-12T17:44:17Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![malmberg](https://avatars.discourse-cdn.com/v4/letter/m/91b2a8/32.png) [@malmberg](https://psychtoolbox.discourse.group/u/malmberg)\ **Post date:** [December 12, 2025, 5:44pm UTC](https://psychtoolbox.discourse.group/t/i-am-recieving-a-value-of-10-for-the-screen-number-when-i-only-have-2-screens/5776/1 "2025-12-12T17:44:17Z")
=== delete this after reading === Please make sure _**[you read this post](https://psychtoolbox.discourse.group/t/posting-guidelines/3058)**_ before asking for help. No one can help you unless you provide a clear description of the software environment you are using and your programming problem… === delete until here === Hi. I am setting up the latest version of PTB on a new machine, and the following function from Lu and Dosher’s text is returning 10 when I only have two screens: whichScreen = max(Screen(‘screens’)); [window p.ScreenRect] = PsychImaging(‘OpenWindow’, whichScreen, p.ScreenBackground); Thus, window is being set to 10. Note I obtain this: Screen(‘screens’) ans = 0 1 2 So why is PsychImaging() returning a window pointer value of 10, which is then deemed out of bounds? ---
**Author:** ![xiangrui](https://avatars.discourse-cdn.com/v4/letter/x/ec9cab/32.png) [@xiangrui](https://psychtoolbox.discourse.group/u/xiangrui)\ **Post date:** [December 12, 2025, 6:53pm UTC](https://psychtoolbox.discourse.group/t/i-am-recieving-a-value-of-10-for-the-screen-number-when-i-only-have-2-screens/5776/2 "2025-12-12T18:53:54Z")
It is just an identifier for the on-screen window, and it seems PTB chose to start with 10 from very beginning.