Pentax 645 DK-80 AF Golden Section Matte focusing screen

Pentax 645 DK-80 Golden Section Matte focusing screen
This is an interchangeable optional focusing screen that may be used with the 645D and 645Z. Unlike the film cameras' operating manuals' renditions of focusing screens, Pentax' 645Z Operating Manual does not provide a description with the screen layout.

We can surmise that the circle represents the spot metering frame. Further, we can surmise that the lines are intended to aid horizontal and vertical alignment. Line lengths short of the edge may indicate the limits of the camera field with the digital sensor.

The spacings of the horizontal and vertical lines define compositional frame elements such that the sizes are in the ratio 1 to 0.618 to 1. (See, for example, https://www.apogeephoto.com/how-to-use-the-golden-ratio-to-improve-your-photography/.)

This screen is reportedly dimensionally identical to the 645N and 645NII screens, so it should fit those camera bodies.