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What does sync with screen option in Key_resp component?

Hi all,
I have used builder to make my experiment (to be uploaded on pavlovia) in which I record participant’s key presses. I need both measures: correct responses and reaction times. I have read all I found about key_resp component (e.g., Keyboard Component — PsychoPy v2021.2), but I can’t find info and understand what does checking the box “sync timing with screen” does?
I am using PsychoPy v2021.1.4. with win 64 bit (windows 7 or 10, depends on pc).
Could you, please, tell me what happens with the recording RTs via keyboard component when the box is checked and when it is not?
I will greatly appreciate your time and help.
Dina.