A1.1.2 A three-field instrument shall show three illuminated
areas in the field of view. Two areas shall be filled with light
transmitted by two different color standards, and these shall be
disposed symmetrically about the third area which shall be
filled with light transmitted by the sample. The rectangular
dimensions of each of the three areas shall be the same, and the
left- and right-hand corners of the full field of view shall be
rounded with radius not exceeding half the vertical dimension.
The illuminated areas shall be separated in a horizontal
direction by vertical lines so that the closest portion of the
sample area and any one of the color standards illuminated
areas subtends the eye of the observer not less than 0.3° nor
more than 0.6°.
A1.1.3 Each i