YSK The three sets numbers on the inside arm of your eyeglasses are in millimeters for: lens width, nose bridge width, and temple length. Adjust size accordingly to your face and its features.
from /r/YouShouldKnow
YSK 眼鏡內臂上的三組數字是以毫米爲單位的：鏡片寬度、鼻樑寬度和太陽穴長度。根據你的臉型和特徵來調整尺寸。