1. Identify the surface finish. It can be distinguished by a black background under a 60 watt incandescent lamp. High-quality products should not have obvious surface defects such as scratches, pitting, chipping, sand holes, water ripples, and bubbles.
2. Place the glasses 33 cm in front of the eyes. When looking at the objects through the glasses, there should be no obvious enlargement or smallness, and there should be no jumping. Otherwise, there is a problem with the quality of the glasses.
3. Through instrument identification, three pieces of constant degrees, no clutter is better.
4. Check whether the trademark, manufacturer, and quality certificate are true and reliable. The lens of the international brand name product is often engraved with the manufacturer's trademark, which can be found by carefully observing the edge of the lens.
A bad flat mirror has some damage to the eyes!