In this guide, the author demonstrates how to decode a QR code by hand, using a pen and paper. The article explains how QR codes contain error correction information, but highlights how this is rarely necessary in practical terms. By breaking down a random example QR code, the author shows how to determine the version of a QR code, identify the format marker, and use the mask pattern to decode the message. The guide also provides tables and diagrams to help with decoding, and addresses common questions and errors in decoding QR codes. The usefulness of this guide may be questionable given the ubiquity of QR code-scanning apps.
https://blog.qartis.com/decoding-small-qr-codes-by-hand/