If this location is set to a value other than zero, the ANTIC starts displaying every line with bit 5 set (enable vertical scrolling) that number of scan line "later", the picture is shifted "up".

VSCROL=0  VSCROL=2 
........  ..####..
...##...  .##..##.
..####..  .######.
.##..##.  .##..##.
.######.  .##..##.
.##..##.  ........
.##..##.  ........
........  .##..##.

........  .##..##.
.##..##.  .######.
.##..##.  .##..##.
.######.  .##..##.
.##..##.  .##..##.
.##..##.  ........
.##..##.  ........
........  ........

If there are several consecutive lines set for vertical fine scrolling (display list instruction with bit 5 set to "1"), the last line to be scrolled has to have bit 5 set to 0, to inhibit lines "jumping" into the screen.

see also: Display List topics, HSCROL