The main reason for using a check jogger is because, when scanning a check, it’s very important for the bottom edge to lay as flat as possible. If one end or the other is crooked, it causes a phenomenon called image skew, or simply skew. It is also a possible source of misfeeds and paper jams.
Image skew can cause parts of the image to be cut off, or for the magnetic ink at the bottom of the check to miss the MICR head that reads key information such as the account and routing numbers. The image at right shows a skew of just 7 degrees, which already causes part of the MICR line to be cut off entirely.
The horizontal inclination of a check jogger is designed to use gravity to help pull the long edge flat as the checks are shaken. It is more important for the bottom edge of a stack of checks to be lined up properly than for the front and back edges. Check scanners can deal with some amount of front-to-back misalignment in the feeder because a part called the discriminator roller ensures that only one check at a time can enter the paper path. This component is sometimes just called the discriminator, or separator.