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B. Fong Chao's article entitled “As the World Turns, II” (Eos, Dec. 3, 1991), was written in an informal manner appropriate for a broad spectrum of readers, many of whom might otherwise have had little interest in the subject of Earth rotation. Unfortunately, the article contains a serious conceptual error concerning the ability of a gyroscope (or “gyrometer”) to sense certain components of the Earth's rotation. The problem begins with the statement that “the gyrometer will record no change in reading so long as Ω is constant in the terrestrial frame (and hence rigidly connected to A) even if it (Ω, the rotation vector of the Earth) actually varies in space, as in the case of the Earth under precession and nutation.”