Hamming Code, how to detect double error?

Question

I know how to detect and correct 1 error, but as i read, to detect double error i need to add one more bit for parity at the end of the message.

So whats next after adding that bit, how can i find out that there is double error?

Answer 1

Simply compute the Hamming code and parity bit from the data, and compare to the transmitted Hamming code and parity bit. If any don't match, you have detected an error.