Not using now of course, but, from memory....
Upright target, start at top
Align bar at 1st line, read (back and forth), UI moves down, you move bar down
Upright target, start read at bottom
Align bar on last line, move UI bar to last, read, UI moves to top, you move bar up one, you move UI down to next to last line....then, you move bar up, UI bar now on last line, you move up one, etc.
upside down target, start at bottom (line #1)
UI is on line #1, bar is placed on line #1 (bottom of upside down page), read, UI moves to #2, you move bar up to line #2, read, etc.