The Bioptic scanner includes a multi-plane scanning ability to capture barcodes no matter the orientation of the object passed by it. This requires the use of scanning through 2 different windows, 1 vertical glass panel and 1 horizontal panel.
The horizontal panel has to take quite a beating from objects being dragged along it throughout its entire lifetime and is made from the strongest scratch resistant, yet optically clear material - Sapphire Glass.
Because diamond is one of the few things that can effectively cut sapphire glass, checkout assistants are generally not allowed to wear diamond rings.