Sapphire crystal: physical and chemical properties of stability, hardness second only to the diamond it can solve the scratch, aging, corrosion and other issues, but fragile. (Usually used for high-end watches.)
Plexiglass: synthetic glass, commonly known as acrylic easy to scratch, but toughness is good, not fragile. (Mostly for low - end watches.)
Mineral glass: anti-wear ability is better, but the anti-vertical combat capability is stronger than sapphire glass, so the military table to use it as a mirror. (Used for low-end watches).
First of all, you can tap your eyes with your fingers and listen carefully. Acrylic mirror will be issued as a plastic sound, and the sound of the glass is thicker. Second, you can judge from the weight point of view, the most light acrylic mirror, sapphire mirror the most important. As the sapphire thermal effect is very good, so when you touch the time, there will be a sense of cold. As the sapphire mirror is much smoother than the other two materials, so if you drop a drop of water on the sapphire mirror, the water droplets are not easy to spread on top, and the other materials will be scattered.