Contents
- Index
How OMR Scanning Works
Response sheets are scanned through an OMR (Optical Mark Reader) or scanner. Scanning with an OMR detects the absence or presence of marks. It does not differentiate between the shape of the marks and cannot recognize hand or machine printed characters.
A scanner has a number of read heads (see Scanner Configuration) which split a response sheet into that number of columns (referred to as tracks). Every response sheet has a clock track. The clock track is used as a control to indicate to the scanner where to check across the response sheet for other marks.
The marks (or lack of marks) identified are then communicated to the application which will interpret them into data.
The way OMR works means response sheets which are overprinted must be correctly aligned (see Overprinting Questionnaires and Printer Alignment). Errors during overprinting may lead to response sheets being unscannable or being scanned but having data incorrectly interpreted.