Use a general unit converter for length, mass, area, and volume. Temperature needs its own formulas; data size needs a clear distinction between decimal units such as MB and binary units such as MiB. Cooking measures may depend on the ingredient, especially when converting volume to mass.
Write the original value with its unit, select the target, and inspect the result's rounding. For an important measurement, convert back or compare a known reference. Do not assume two similar unit labels mean the same thing.
Keep units attached to the numbers throughout.
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