RX100 dual pivot caliper.What is the small adjuster screw for?

[Paulus]

I throw myself on the collective here.
I have had the bike from new, 26 odd years now, with these RX100 dual pivot brakes. But, I have never known what the adjuster screw on the top actually adjusts as I have never touched them.
Can someone please enlighten me.

 

[Ian H]

To align the brake blocks, set them equidistant from the rim.

 

[Paulus]

To align the brake blocks, set them equidistant from the rim.

Thankyou. So it is of a centering adjuster.