It's the relationship between online and offline.
On-line means that the float glass has been coated. Bond firmly to glass
Offline is coated after float glass and tempered glass are produced.
Generally, off-line coating film and glass bonding is not very strong, when making hollow glass, it is necessary to remove the film for the sake of glass performance and safety. (Of course, many processing plants do not remove it.)
Generally, the film surface of off-line coating is very fragile and can not be tempered.
However, the off-line processing equipment is simple, does not need the huge equipment support, and the color system is rich, online color is relatively single. Sometimes the transmittance of two batches of glass differs by 15 degrees.