The index of the eventEntry that is
used when a rising threshold is crossed. The
eventEntry identified by a particular value of
this index is the same as identified by the same value
of the eventIndex object. If there is no
corresponding entry in the eventTable, then
no association exists. In particular, if this value
is zero, no associated event will be generated, as
zero is not a valid event index.
This object may not be modified if the associated
alarmStatus object is equal to valid.