Thats a brightness level measurement, they are making REAL D send field auditors to check. This is likely a James Cameron requirement to sniff out bad 3D presentations ahead of AVATAR 2.
Fox is mandating that all screens showing ALITA in 3D must meet a minimum 4.5fl standard, will not license 3D showtimes to those that can'tnotfabioJan 19, 16:18