How do Barcodes work ?

A barcode is a really simple idea: give every item that you want to classify its own, unique number and then simply print the number on the item so an electronic scanning device can read it.

We could simply print the number itself, but the trouble with decimal numbers is that they're easy to confuse (a misprinted eight could look like a three to a computer, while six is identical to nine if you turn it upside down—which could cause all sorts of chaos at the checkout if you scanned your cornflakes the wrong way up).

What we really need is a completely reliable way of printing numbers so that they can be read very accurately at high speeds. That's the problem that barcodes solve.

What we really need is a completely reliable way of printing numbers so that they can be read very accurately at high speeds. That's the problem that barcodes solve.

If you look at a barcode, you probably can't make head or tail of it: you don't know where one number ends and another one begins. But it's simple really.

Each digit in the product number is given the same amount of horizontal space: exactly 7 units.

Then, to represent any of the numbers from zero through nine, we simply color those seven units with a different pattern of black and white stripes.

Thus, the number one is represented by coloring in two white stripes, two black stripes, two white stripes, and one black stripe, while the number two is represented by two white stripes, one black stripe, two white stripes, and two final black stripes.

Thus, the number one is represented by coloring in two white stripes, two black stripes, two white stripes, and one black stripe, while the number two is represented by two white stripes, one black stripe, two white stripes, and two final black stripes.

You've probably noticed that barcodes can be quite long and that's because they have to represent three different types of information.

The first part of a barcode tells you the country where it was issued. The next part reveals the manufacturer of the product.

The final part of the barcode identifies the product itself.

Different types of the same basic product (for example, four-packs of Coca-Cola bottles and six-packs of Coca-Cola cans) have totally different barcode numbers.

Most products carry a simple barcode known as the UPC (universal product code)—a line of vertical stripes with a set of numbers printed underneath it (so someone can manually key in the product number if the barcode is misprinted or damaged in the store and won't scan through the barcode reader).

There is another kind of barcode that is becoming increasingly common and its stores much more information. It's called a 2D (two-dimensional) barcode) and you sometimes see it on things like self-printed postage stamps.

Different types of barcode scanners are available for all kinds of applications. In small, convenience stores, you'll typically find a basic wand scanner.

The simplest ones look like electronic pens or giant, oversized razors.

They shine red LED light onto the black and white barcode pattern and then read the pattern of reflected light with a light-sensitive CCD or a string of photoelectric cells.

If you have a pen scanner, you have to run it across the barcode so it can reach each block of black or white in turn; with a wand scanner, the CCD or photocells read the entire code at once.

In a busy superstore, you're more likely to see a very sophisticated laser scanner.

It'll be built into the base of the checkout lane, under a piece of glass, and you may be able to see the laser beam being bounced around at high-speed by a spinning wheel so it reads products (literally) in a flash.

Another technology uses a small video camera to take an instant digital photograph of the barcode.

A computer then analyzes the photograph, picking out only the barcode part of it and converting the pattern of black and white bars into a number.

(Barcode-scanning apps that run on cellphones work this way, using the phone's built-in camera to photograph the code.) Scanners like this can accurately read dozens of products waved past them each minute and are far more accurate than old-style checkouts (where you have to key in the price of every item by hand).

The best barcode scanners are so accurate that they make only one mistake in something like 70 million pieces of scanned information! (Compare that to typing on a keypad, where you're typically likely to make one error in every 100 characters you type.)