A time-based amount of time, such as '34.5 seconds'. !(p) This class models a quantity or amount of time _in terms of seconds and nanoseconds. It can be accessed using other duration-based units, such as minutes and hours. In addition, the {@link ChronoUnit#DAYS DAYS} unit can be used and is treated as exactly equal to 24 hours, thus ignoring daylight savings effects. See {@link Period} for the date-based equivalent to this class. !(p) A physical duration could be of infinite length. For practicality, the duration is stored with constraints similar to {@link Instant}. The duration uses nanosecond resolution with a maximum value of the seconds that can be held _in a {@code long}. This is greater than the current estimated age of the universe. !(p) The range of a duration requires the storage of a number larger than a {@code long}. To achieve this, the class stores a {@code long} representing seconds and an {@code int} representing nanosecond-of-second, which will always be between 0 and 999,999,999. The model is of a directed duration, meaning that the duration may be negative. !(p) The duration is measured _in "seconds", but these are not necessarily identical to the scientific "SI second" definition based on atomic clocks. This difference only impacts durations measured near a leap-second and should not affect most applications. See {@link Instant} for a discussion as to the meaning of the second and time-scales.