Posts tagged ‘cc’

Credit Cards Reveal Hidden Symbols Under Black Lights

By Chad Upton | Editor

Many people know that paper money has markings that illuminate under a black light. These markings make it more difficult to counterfeit and thus easier to spot counterfeit money. Also, regular paper glows wildly under a black light, while currency paper does not, another dead giveaway. The same also applies to credit cards.

For this demonstration, I rounded up one card from each of the major issuers and tore my basement apart looking for my standard issue college black light. I eventually found it, but only after creating a small pile of retro items for this year’s halloween costume.

The black light’s strong purple glow catalyzed the American Express card to reveal “AMEX” spelled across the card, with a picture of a globe between “AM” and “EX.”

MasterCard was hiding “MC” on theirs:

The Visa card revealed the V logo.

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August 12, 2011 at 2:00 am 4 comments

The Meaning of the Digits on Your Credit Card

By Chad Upton | Editor

There are thousands of different credit cards from the major issuers, but all of them have one thing in common: the meaning of the numbers on the card.

Most major cards have 16 digits on them and each number has a specific meaning.

Digit 1 (Industry ID)

  • 1 and 2 are Airline cards
  • 3 – Travel and Entertainment
    • ex. Amex
  • 4, 5 – Banking and Financial
    • ex. Visa, Mastercard
  • 6 – Merchandising and Banking
    • ex. Discover, Diners Club
  • 7 – Petroleum
  • 8 – Telecom
  • 9 – Misc.

Digits 2-6 (Issuer ID)

Although all Visa cards start with the number 4, the following 5 digits indicate which bank that issued the Visa card. Mastercards start with 5, Discover starts with 6. You’ll notice that some websites don’t ask you what type of card you have — they obviously know what the digits on the card mean.

Digits 7-15 (Account ID)

The unique number that identifies your account.

Digit 16 (Checksum)

This single digit is one of the most important ones on the card. Much like the last digit of a barcode, the sole purpose of this digit is to allow validation of the rest of the number. In other words, there is a mathematical relationship between the numbers on the card, so if the number is entered incorrectly, the card validator system can indicate the card number was entered incorrectly.

You can validate a card number on your own too. Double every other number, starting with the first number. Add the result of those multiplications to all of the other digits on the card, treating all numbers as individual digits, including double digit results from the doubling operation. If the sum of all these numbers is divisible by ten, the number is valid according to the ISO standard. However, a valid card number doesn’t necessarily mean the number is an active account or that charges can be made with it.

In the early days of credit cards, they didn’t actually check this before imprinting a card for small purchases and larger purchases were verified with a phone call. Today, it’s usually done electronically. When your card is swiped, the number is validated by the point of sale system (using the method above) and if the card number is valid then an electronic request is sent to verify the charge will be accepted by the card issuer.

Some retail stores will ask to see your card so they can manually type in the last four digits on the card. This verifies that the number embossed in the card is the same number that is programmed to the magnet stripe on the back; this is one way retailers can catch counterfeit or reprogrammed cards before the goods leave the store.

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Sources: Abby’s Guide, HowStuffWorksMerriam ParkMint

February 7, 2011 at 2:00 am 12 comments

The White Dashes at the Top of a TV Picture

By Chad Upton | Editor

They may appear as rapidly flashing dots, dashes, lines or boxes across the top of your TV screen.

The white lines are more prevalent on HDTVs, although they can show on older standard definition sets too.

They often appear while watching an HD channel that is broadcasting a standard definition signal, which frequently happens during commercial breaks and shows that are not available in high definition.

The lines are supposed to be there, you’re just not supposed to see them. If you have seen them, they will vary in size and shape depending on your TV.

These lines are like barcodes embedded in the picture. Closed captioning, teletext and programming guide information is represented by these white lines. Your TV can interpret them and display the information in a format that you can read.

Although this primarily affects HDTVs, it stems from variances in old Tube TVs (Cathode Ray Tubes). In the early days of television, there were extreme variances in production of television sets — some would cut off more of the picture than others.

Broadcasters overcame this problem by trying to keep all titles and important actions away from the very edges of the screen, in case they were cut off on some TVs. That extra space that you don’t see is called the overscanned image (because of the way that CRTs would paint an image on the screen by scanning side to side sixty times per second).

The overscan area became a good place to hide extra information when closed captioning data was added to TV signals.

HDTV signals do not overscan. Their signals are newer and were designed to encapsulate extra information from the beginning. But, you may still see these lines on an HDTV if the broadcaster is showing content that has the lines.

Most good televisions have the option to adjust overscan, including hdtvs. You’ll have to consult your manual, but this option will allow you to adjust the picture so the white lines are not visible.

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Sources: Wikipedia (Safe area, Overscan)

August 20, 2010 at 5:00 am 1 comment


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