How do the lines on a bar code and a scanner of bar codes work?

Most bar codes you will see on consumer products have the numbers below.

A Bar code is a way of making information readable to a machine.

It does this, similar to Morse Code, by encoding normal letters and numbers as patterns of thick and thin black lines.

The purpose of the bar code is to tightly control the comparison between the thick and thin lines, and the space in between, so that the pattern has a high chance of being read correctly.

Every letter in the alphabet has a corresponding bar code character, when the bar code reader scans the bar code its electronics translate the bar code into the letters, and send these letters in machine code to the computer.

Some bar code readers use what is called a "wedge" - they are plugged in between the keyboard and the computer, and send signals into the keyboard port of the computer exactly as if the operator had typed in the numbers on the bar code.