As OCR does not have any error correction - e.g with a DataMatrix code - there is no guarantee that the OCR is 100% correct every time.

If the application is dependent on the OCR being 100% correct then the OCR should be linked to a machine-readable code that does have error correction and so can be relied upon to be 100% correct.

The purpose of the linked field function is to check that two fields are identical so if, for example, a 3 is read as an 8 using the OCR then the difference will be detected in the linked field.