Some astronomical research, including Frogel's on cool, water-bearing stars, requires that level of accuracy. Frogel's work originated from a calibration question.
Astronomers observing directly overhead do so through a known, and very thin, atmospheric layer.
But a star near the horizon would appear dimmed due to the much thicker depth of air. But sometimes astronomers rely on standard tables instead of their own measurements. Astronomers observing a star low on the horizon must look through a much greater atmospheric thickness than if the star were directly overhead. Such stars can appear dimmer. Extra moistrure in the air during periods of El Nino further complicates the measurements.