Besides the OCR engines, the OCR engine list of a zone (Read settings of the zone, or the Object Properties menu of the Indexing tab) offers two special readers for fields that need extra certainty or that are not text at all.
Dual OCR (ChronoScan + Tesseract)
The zone is read twice, with the ChronoScan OCR engine and with Tesseract. If both engines return the same value the field is accepted; if they disagree the field is flagged with a validation error ("dual OCR mismatch") and the operator has to confirm it. Use it on critical fields such as amounts, account numbers or identifiers where a silent OCR error is expensive. The cost is a second OCR pass on that zone only.
Mark Detection does not read characters: it measures how much of the zone is filled with ink and decides whether the mark is present. It is the tool for check boxes, option boxes, signature boxes and any "is there something here" field (OMR). Draw the zone exactly over the box and set:
Algorithm: Threshold Level (percentage of dark pixels in the zone) or Entities count Level (number of connected ink objects found in the zone, better for signatures and hand marks).
Trigger level: the value from which the mark is considered present. Set it to -1 to see the raw measurement in the field ("-1 shows the reading") and calibrate it on marked and unmarked samples, then set the final level.
Positive value and Negative value: the text written to the field when the mark is present or absent (for example Yes/No or 1/0).
Load and Save default: keep a calibrated set of values to reuse on other zones.
Mark Detection zones are usual in forms and in capture grids (one column of check boxes per row). The guide Checkbox Detection with Data Grids shows a complete example. Image processing (deskew, despeckle) before the reading improves the stability of the measurement.
