micrometremicrometern.

1880 Jrnl. Royal Microsc. Soc. 3 327 The same reasoning..leads us, however, to recommend the adoption of ‘micrometre’ instead of ‘micromillimetre’, which would secure the uniformity desired, besides being a more convenient word.

1934 Science 23 Feb. 184/1 A more serious error is often made in the conception of the micro-meter, which is a millionth of a meter and not a thousandth of a millimeter.

1965 New Scientist 24 June 868/2 A human kidney contains approximately one million units called nephrons, each consisting of a thin tube about 20 to 50 micrometres wide and 50 millimetres long.

1968 Nature 16 Nov. 651/2 By resolution No. 7 the conference [sc. the thirteenth General Conference of Weights and Measures] decided to proscribe further use of the name ‘micron’, with the symbol μ attributed to this name, for the millionth part of the metre. The symbol μ is now the recognized prefix for the decimal sub-multiple 10⁻⁶ and the appropriate name for the millionth part of the metre is ‘micrometre’, with symbol μm.

1973 Physics Bull. Nov. 662/3 They contain solid particles..with dimensions of about a tenth of a micrometre, a mass of 10⁻¹⁵ g each.

1989 Sci. Amer. Nov. 12/1 The majority of aquatic microorganisms were once thought to be nanoplankton, tiny organisms measuring no more than 10 or 20 micrometers in diameter.

1995 Daily Tel. 6 June 18/4 This increases the accuracy of the laser beam, allowing the ‘pits’ that contain the digital signals to be 0.4 micrometres across, compared with 1.1 micrometres on CDs.