To the Editor: In the CPC of September 2, a computerized tomogram (CT-scan) is reported as showing “a 23 to 58 μm high-absorption abnormality,” and I wish to take exception to the abbreviation employed. In physics and engineering, μm is the internationally defined symbol for micrometer (10–6 meter), a unit of length that, in the biologic literature, is simply known as the “micron.” The symbol in question is, in fact, correctly used in the same CPC to label the scales for the electron micrographs in the article. The numerical printout of the CT-scan consists of an array of absorption. . . No extract is available for articles shorter than 400 words. © 1976, Massachusetts Medical Society. All rights reserved.