水晶石石英断片，直径4到64毫米（0。16到2。51英寸），尤指天然圆形的石英颗粒 A rock fragment between4 and64 millimeters(0.16 and2.51 inches) in diameter, especially one that has been naturally rounded.
光度视网膜亮度单位，相当于每平方米有一烛光亮度的表面，通过一平方毫米的瞳孔区域，到达视网膜的光线数量 A unit of retinal illumination, equal to the amount of light that reaches the retina through 1 square millimeter of pupil area from a surface having a brightness of 1 candela per square meter.
这边缘必须切割到0.02毫米的精密度。 The edge must be machined to 0.02 millimeters.