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personal equation[′pər·sən·əl i′kwā·zhən]
a term used in astronomy to designate observational (measurement) errors resulting from the physical properties of the observer, that is, personal errors. Personal equations are of the nature of systematic errors. They may vary to some degree under the influence of variations in the physical state of the observer, the conditions of observation, the method of recording the values being measured, and other factors. The magnitude of the personal equation in astronomical observations also depends on the brightness of the observed celestial object and the speed with which its image crosses the telescope’s field of view. The existence of personal equations was discovered at the end of the 18th century, and they were first studied by F. Bessel and V. Ia. Struve. A detailed study of them was conducted in the 1870s by N. Ia. Tsinger.