system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do QR codes work, and why can my phone recognize one before I get the entire thing in view of the camera?
gpt
QR codes work in quite a complicated way, but the short answer is that they're designed to continue working even if damaged. You can cover something like 1/3 of the code and it'll still read, which is how the QR codes with logos and things in the centre still work - they aren't cleveley generated, they're just slapping the image in there and trusting to maths that it'll still work. 

That's why the phone can read it before seeing the whole thing - it's using the redundancy built into the code.