Here is another photo with more detail. See attachment.
Thought not shown in photo, the pivot point is supposed to be located 25% of the distance between tack and leech.
This is so there is sufficent pressure on the jib boom to maintain tension on the jib boom topping lift,
(the line you see at the back of the boom with small black plastic adjuster).
The purpose/adjustment of the jib boom topping lift is to match to curvature of jib leech to the main leech,
thereby maintaining a uniform slot.
The slot width/opening is adjusted by the jib sheet.