OMR is based around a predefined form such as the one above. The form will have specific parts for someone to fill out by putting a pencil mark in the correct box.

The above example is from a multiple choice exam. A special reader will then read in this form and be able to tell what was marked. If two marks are made in the same section then the reader will only accept one of the answers, most likely the first one. Also if the mark does not cover the whole of the circle then the reader may miss it.

This type of input is used for multiple choice exams and registers as they can be automatically be marks and processed. It is not suitable for any form of written communication.