When data is input using a manual input device such as a keyboard, errors often occur due to values being entered incorrectly.

A common mistake is to swap two letters or digits around; this is called a transposition error.

One method that can be used to cut down on errors like this is to use coded values for data.

Suppose that a field could contain one of three possible values; small, medium or large. Instead of typing in the full word each time we could instead type S, M or L.

The advantages of coding values 

• Fewer key presses are needed when entering a value in the field so there is less chance of the wrong keys being pressed;
• Time is saved when entering data because there is less to type in each time;
• Database packages allow automatic validation checks to be set up to make sure that only the allowed codes have been input in a field.