The clock enters the set state when SET CLOCK causes
the clock's contents to be set, that is, when SET CLOCK is
executed without encountering any exceptions and with
the clock operational and the clock-security switch in the
enabled position. The clock can be placed in the set state
from either the not-set or the error state.
The clock enters the error state whenever the clock stops
or misses a time increment, such as may occur when the
power supply is temporarily disconnected, or when a
malfunction is detected that is likely to have affected the
validity of the clock's value.
The operation of the clock is interlocked such that
successive executions of STORE CLOCK do not provide
the same clock value unless the clock validity indicator is
off or the clock value has been changed in between by
execution of SET CLOCK.