Error control-Parity

Parity

The following is a demonstration example of error detection 

The first photo shows the random 25 cards in a grid

The second photo shows the grid with redundant bits added

The final photo shows the grid with an error added

With a partner, unfamiliar with the trick, get them to set up the cards in a grid 5 by 5 using the double sided cards (black and white, representing bits of zero and one ). Make sure they have a random order of cards, ie not all one colour. Then complete the parity grid by adding  redundant bits for error detection (sixth row to the top and side of the grid); but in doing so complete each sixth row and column so there is an even number of black and white. Then ask your partner to tamper with the grid, you will then be able to detect any errors with the check equation (in each row bits are even). This is because if any of the cards change then the number of each colour in that row, will no-longer be even. This will then show if there is a  need for error correction. This technique is used in all kinds of computer applications we use everyday, for example if you try to open an Excel file in word, the program will have a reconisation system incorporated into the saved data to distinguish between Microsoft's other data types. This system will also most likely test to see if the file is damaged too. This could be achieved in a similar way to the demonstration with the parity cards, the program could add bits too the end of the text using a formula, like in the demonstration but more complex; this will communicate the necessary information to the program to give the user useful feed back rather than confusing them with an unrecognizable data representation.