HP 3000 Manuals

HP ALLBASE/4GL Developer Reference Manual Vol. 1

Available Space Keys 

The  Available Space  function key is in the Main Keys function key set
for menus.  For data screens and windows, the  Available Space  function
key is in the Sequence Numbers function key set.

The available space function key displays the amount of space (in
characters) between the current cursor position and the beginning of the
next field.  It also displays the details of the field or system item at
the cursor position if the item has been temporarily shortened due to a
clash with another item.

MPE/iX 5.0 Documentation