How to use the 8-character blind plate? What is the standard of the 8-character blind plate?

Figure-eight blind plate, figure-eight blind plate, flat figure-eight blind plate What is figure-eight blind plate, concave-convex figure-eight blind plate?

Pressure display of concave-convex figure-eight blind plate: concave-convex figure-eight blind plate: PN 1.6MPa BLF, concave-convex figure-eight blind plate: PN2.5MPa BLF, concave-convex figure-eight blind plate: PN4.0MPa BLF, concave-convex figure-eight blind plate: PN 10.0.