Pentax 67 Operating Manual page 40

Besides the standard microprism screen, there
are four types of focusing screens as follows;
(1) Split Image,
(2> Matte with Central Open Spot,
(3) Grid with Microprism,
(4) Grid with Matte
The replacement should be performed at the
nearest Pentax service facility.
Focusing with split image;
The image is in focus when the images
above and below the split line up.
Focusing screens with grid:
The grid is useful to check the horizontal or
vertical lines in an image are parallel. The
horizontal and vertical lines are spaced at
9mm.
For precise focusing, this compact magnifier
provides two times enlargement of the central
area. Includes a built-in diopter adjuster.