Signed integer indicating the precision
of the system clock, in seconds to the nearest
power of two. The value must be rounded to the
next larger power of two; for instance, a 50-Hz
(20 ms) or 60-Hz (16.67 ms) power-frequency clock
would be assigned the value -5 (31.25 ms), while a
1000-Hz (1 ms) crystal-controlled clock would be
assigned the value -9 (1.95 ms).