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+@node Constants
+@chapter Constants
+
+@file{<libred.h>} defines a number of symbolic constants
+suitable for using a @code{#if} preprocessing directives.
+
+@table @code
+@item LIBRED_SOLAR_APPARENT_RADIUS
+The approximate apparent size of the Sun in degrees.
+This value should be about 0.5(3).
+
+@item LIBRED_SOLAR_ELEVATION_SUNSET_SUNRISE
+The Sun's elevation at sunset and sunrise, measured in
+degrees. This value will always be 0.0.
+
+@item LIBRED_SOLAR_ELEVATION_CIVIL_DUSK_DAWN
+The Sun's elevation at civil dusk and civil dawn, measured
+in degrees. This value will always be @math{-6.0}.
+
+@item LIBRED_SOLAR_ELEVATION_NAUTICAL_DUSK_DAWN
+The Sun's elevation at nautical dusk and nautical dawn,
+measured in degrees. This value will always be @math{-12.0}.
+
+@item LIBRED_SOLAR_ELEVATION_ASTRONOMICAL_DUSK_DAWN
+The Sun's elevation at astronomical dusk and astronomical
+dawn, measured in degrees. This value will always be @math{-18.0}.
+
+@item LIBRED_HIGHEST_TEMPERATURE
+The highest temperature, in kelvins, for which there is a
+colour temperature in the table of colour temperature. Any
+temperature above this is automatically truncated by
+@code{libred_get_colour}, as higher values shall be
+unnoticeable. Currently, this value is 40@tie{}000.
+
+@item LIBRED_LOWEST_TEMPERATURE
+The lowest temperature, in kelvins, for which there is a
+colour temperature in the table of colour temperature. Any
+temperature below this results in @code{libred_get_colour}
+failing and setting @code{errno} to @code{EDOM}. Currently
+this value 1000, hypothetical changes will be very small.
+
+@item LIBRED_DELTA_TEMPERATURE
+The temperatures differences between sequential colour
+temperatures in the colour temperatures look up table.
+Currently this value is 100.
+@end table
+