What a mirror-split actually measures, why nobody is 50/50, and what the percentage should mean to you.
Every face tool offers the split-screen mirror. Few explain the number. Symmetry scores compare left pixels against mirrored right pixels — a blend of bone structure, muscle habit and how you were photographed.
Typical scores sit far from 100%: faces average noticeable asymmetry, and portrait photographers correct for it by posing the 'better' side. The number is descriptive, not a grade.
Photo-side choice, part placement and chewing-side habits move the needle a little. The rest is bone structure — and every ranked 'beautiful' face in portrait history is asymmetric too.