Effect of geotropism on instrument readings. Calibrating survey meters to account for geotropism is discussed.

Geotropism is an analog meter's response due to orientation in a gravitational field whether radiation is present or not. For a conventional analog meter, the geotropic response is reflected in the movement of the meter needle. Geotropism is not relevant for digital portable survey (e.g., liquid crystal displays) or stationary bench top meters. The degree of geotropism must be evaluated during type testing and routine calibration when dealing with portable survey instruments. Geotropism is defined in , , and as a change in instrument reading with a change in instrument orientation as a result of gravitational effects. Ideally, the manufacturer when selecting a meter movement for a particular portable survey instrument application considers geotropism in their selection. However, simply employing high quality meters in the manufacture of instruments is not sufficient, since survey meters may be damaged to the point that geotropism may be exhibited. Awareness of geotropism and the ability to recognize its occurrence are invaluable to radiation protection technologists, especially those who calibrate or evaluate survey instruments in the course of doing their job.