Blog post about one preferred encoding to represent the μ-sign (#2757)

Author: jbouwh

blog/2025-08-20-micro-sign-encoding.md

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+---
+author: Jan Bouwhuis
+authorURL: https://github.com/jbouwh
+authorImageURL: https://avatars.githubusercontent.com/u/7188918?s=96&v=4
+title: Standardize encoding of μ in units of measurement
+---
+
+## One preferred encoding to represent μ in units of measurement
+
+The unit prefix μ is used by unit of measurement constants like μV and μS.
+There are however two different Unicode encodings of μ:
+
+1. The [MICRO SIGN](https://www.compart.com/en/unicode/U+00B5)
+2. The [Greek Small Letter Mu](https://www.compart.com/en/unicode/U+03BC)
+
+Home Assistant previously mixed the two encodings, which caused issues because string comparisons between the two encodings would fail causing unit of measurement validations to fail.
+
+We chose the "Greek Small Letter Mu" because the "MICRO SIGN" encoding is there for compatibility with old 8-bit western European character sets, and the unicode consortium recommends against using it.
+
+With [#144853](https://github.com/home-assistant/core/pull/144853) we have fixed this in the core of Home Assistant by consequently using the Greek Small Letter Mu version to encode μ. In Python literal strings this variant is encoded as `"\u03bc"`.
+
+Developers should check if their code and libraries have a dependency with the ambiguous MICRO SIGN (μ) `"\u00b5"`, and migrate their code to use the Greek Small Letter Mu `"\u03bc"` instead to avoid issues.
+
+The `sensor` and `number` entity platforms now include a built-in feature to automatically convert units that use the ambiguous MICRO SIGN (μ) encoding.
+
+## Find instances in Visual Studio Code
+
+In Visual Studio Code, enable **Match Case** in the **Search** (files) panel to find only the chosen encoding. Copy the exact μ character from above and paste it into the search box. The editor’s page search matches all variants; use the global search instead.
+## New linter
+
+To avoid issues with new or changed code, [#144853](https://github.com/home-assistant/core/pull/144853) adds a linter that warns about incorrect literal assignments using the non-preferred encoding of μ.