In order for FORMS to identify and process a form, the form must contain at least three and preferably five separate, unique objects or intersections of lines that can be used in adjustment fields.
Any object can be used as an adjustment object, if it:
Is larger than 2 mm and smaller than 10 mm in height (3/32" to 3/8")
Has good contrast with its background
Is not written on or covered up when the form is filled in
Is not next to another adjustment object (adjustment objects must be as far away from one another as possible, ideally one at each corner of the form and one in the middle)
Is not extremely close to other characters or lines
Is not near an identical object
Is not so near the edge of the form (closer than 1 cm or 3/8") that FORMS might miss it
When a form is scanned, FORMS checks each adjustment object’s size, position and shape. If three adjustment objects found on the form are identical to the ones you defined on a form definition included in the job description being run, the form is positively identified.
If FORMS is to identify forms that are rotated 180 degrees, the adjustment fields must not be the same when the form is rotated 180 degrees as when it is not rotated. More info.
In spite of this long list of requirements, it is rarely a problem to find such objects on a form.
Defining a traditional adjustment field
How FORMS identifies forms that have traditional adjustment fields