It is controlled by the '''Enable View Parent''' permission available within [[Visibility_Permissions#UTA-level_Visibility_Permissions|UTA Feature and Function Permissions]].
https://wiki.smartsimple.com/index.php?title=Split_Screen&action=edit#
If your role has the permission set against a UTA then when you access a level 2 or 3 record then you will see a small icon along the top of the page.
[[Image:SplitScreen1.png|450px|border]]
[[Image:SplitScreen2.png|950px|border]]