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ANSI Common Lisp  25 Environment 25.1 The External Environment
25.1.4 Time
Time is represented in four different ways in Common Lisp:
decoded time,
universal time,
internal time,
and seconds.
Decoded time and universal time are used primarily to represent calendar time,
and are precise only to one second.
Internal time is used primarily to represent measurements of computer
time (such as run time) and is precise to some implementation-dependent
fraction of a second called an internal time unit,
as specified by internal-time-units-per-second.
An internal time can be used
for either absolute and relative time measurements.
Both a universal time and a decoded time can be used
only for absolute time measurements.
In the case of one function, sleep,
time intervals are represented as a non-negative real number of seconds.
The next figure shows defined names relating to time.
25.1.4.1 Decoded Time
25.1.4.2 Universal Time
25.1.4.3 Internal Time
25.1.4.4 Seconds
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