> Is "μμ" really the Greek abbreviation for millimetres ? If so,
No of course not! People write some χιλ. or even χιλιοστόμετρα.
> how do the Greeks abbreviate micrometers (= microns, "μ") ?
they do not abbreviate it since since newspapers either use
μικρόμετρο or μm.
Α.Σ.
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Apostolos Syropoulos
Xanthi, Greece