Sekonic SR-1800 Operating Manual page 50

Writing implements
Readable marks and unreadable marks depend on the writing instruments used. This can also
differ according to the light source that the reading sensor uses.
Relationships between sensors used for OMR (light source) and writing implements
Light source
Color tone
wavelength
940nm
Infra red
(standard)
660nm Visible light
(*Option) (red)
Hopper
Place where readable sheets are set.
Readable mark colors
and writing implement
Color: black (pigment)
Writing implement: pencil
Color: black, brown, blue, green, purple
Writing implement: pencil, fountain pen,
water/oil base ballpoint pen, water/oil
base marker
Unreadable mark colors
and writing implement
Color: other than black
Writing implement: other than pencil
Color: red, orange, yellow
Writing implement: items in above
colors
SR-1800