Micro Sign vs Greek Mu

The micro sign (µ, U+00B5) is a Latin-1 Supplement character historically included for compatibility with legacy encodings, while the Greek small letter mu (μ, U+03BC) is the genuine Greek letter from the Greek and Coptic Unicode block. Visually they are essentially indistinguishable in most fonts, but they are distinct code points that will not match in string comparisons, regular expressions, or database queries — a common source of hard-to-diagnose bugs in scientific software. The Unicode standard itself recommends using the Greek small letter mu (U+03BC) for the SI prefix micro- (as in μm for micrometers or μs for microseconds) rather than the compatibility micro sign. Unicode normalization (specifically NFKC or NFKD) will map the micro sign U+00B5 to Greek mu U+03BC, so normalized text will always use U+03BC; this is one of the few cases where normalization changes a character's identity. When copying μ from scientific papers or web pages, always check the actual code point in a Unicode inspector, since sources vary inconsistently between the two.