A scannable form for use in an optical mark reading system has a timing track that is pre-encoded with data information known or determined prior to a respondent completing the scannable form. The data information is pre-encoded in the control mark column on the scannable form by utilizing that portion...http://www.google.se/patents/US5184003?utm_source=gb-gplus-sharePatent US5184003 - Scannable form having a control mark column with encoded data marks
