Have a look here to see what goes where, there is absolutely no need to memorize the entire grid. I am basically saying that:
You can do this without memo phase and just read the number on the actual code… you just need to check the mask and error correction in use then start reading the number from the bottom right… almost half the code has no useful information
Here is a larger diagram showing the “unmasked” QR code. Different regions of the symbol are indicated, including the boundaries of the message data bytes.
So check “Format Info” (red) and “Format Error Correction” (orange), unmask the message (gray) and just write down the numbers (Message Data Bytes).
Writing one by hand is actually more difficult… you need to know Galois fields for the error correction part that you need to include. I used to handwrite (pen and paper) “Hello” as a QR code when explaining the logic… never memorized the bits for it though.
The coolest part is actually Évariste Galois himself, who died aged 20 in a duel roughly 200 years ago… he happened to be very friendly with someone else’s wife. He also spent quite some time in prison but let’s non forget basically laid the foundation for today’s group theory. 