proc GetNextUpDown(NewPosition$)
  local(RasterIndex$, TempSize$, TempStr$);
  
  RasterIndex$ = 0;
  TempSize$ = RasterSizes$[RasterIndex$];
  while (TempSize$ != 0)
    if (TempSize$ == NewPosition$)
      if (RasterSizes$[RasterIndex$+1] == 0)
        RasterNextUpPtSize$ = NewPosition$;
      else
        RasterNextUpPtSize$ = RasterSizes$[RasterIndex$+1];
      end;
      if ((RasterIndex$ - 1) < 0)
        RasterNextDownPtSize$ = NewPosition$;
      else
        RasterNextDownPtSize$ = RasterSizes$[RasterIndex$-1];
      end;
      break;
    else if (TempSize$ > NewPosition$)
      RasterNextUpPtSize$ = TempSize$;
      if ((RasterIndex$ - 1) < 0)
        RasterNextDownPtSize$ = NewPosition$;
      else
        RasterNextDownPtSize$ = RasterSizes$[RasterIndex$-1];
      end;
      break;
    end;
    TempSize$ = RasterSizes$[++RasterIndex$];
  end;
  tempStr$ = apichar(str(RasterNextUpPtSize$));
  SetWindowText(NextUpSize$, tempStr$);
  tempStr$ = apichar(str(RasterNextDownPtSize$));
  SetWindowText(NextDownSize$, tempStr$);
end;