Sekonic SR-1800 Operating Manual page 48

Direct under type
If the sheet has pre-printed timing marks, the scanning area (reading area) of targeted mark
frames will be determined by such timing marks.
Direct under type refers to a method of reading a zone that is the same as the timing mark
width.
Other methods include timing control type and mark to mark type.
Timing mark Timing mark
Transmission interface
The hardware connecting a computer and the OMR, in other words the mediating connection.
The SR-1800 uses USB or RS-232C interfaces.
Dropout color
Refers to colors pre-printed or written on documents that people can see but that don't appear
when read with an image scanner or other devices.
There are "warm colors" and "cold colors" by appearance. Warm colors called orange end, red
end, etc. are used as OCR dropout colors, and you need to switch filters in this device for bluish
dropout color sheets such as the standard forms used by the Japan Chain Stores Association.
Bluish colored lines drop out when they are scanned with copy machines and other devices
even if they don't use dropout color ink. OCR sheet for fax machines uses "cold color (blue-
green)" dropout colors, but there are only a few colors that can be used with most fax machines,
because they are different from OCR units.
(1) Dropout color print darkness is controlled by the PCS value. There are two ways to measure
PCS, black backing and white backing, and you should pay attention because they differ
depending on the model.
(2) OCR sheets are generally used for printing character boxes using dropout color inks and
printing letters in clear areas.
(3) Recently, some models have become available that are capable of reading black character
boxes, but dropout color printing sheets are often superior in both recognition performance
and processing speed.
(4) Dropout colors are chosen by spectral characteristics and PCS values that are determined
by scanner sensor, light source, and filter.
Mark frame Mark frame
SR-1800
Reading area Reading area