Originally posted by burrd I have clicked it a couple times before just to see what it does. It seems to set the meter graph in the camera so that the correct exposure for what you are looking at is your current SS and A. So you could theoretically be looking at the sun with 3200 speed film 1 second exposure at f/2 and press the button and the graph sets that as the correct exposure. .
It is exposure compensation which on that camera will allow +3/-3 adjustment. It is not a magic button that allows correct exposure of the sun or any other bright object.
Here is a link to the manual....
https://www.pentax-manuals.com/manuals/af/z20.pdf