We assume that, apart of the monitoring device, our system
evolves under time evolution described by the Schrödinger
equation with a self--adjoint Hamiltonian 
. We denote by
the corresponding unitary propagator.
Again, for simplicity, we will assume that 
does not
depend explicitly on time.
Our second postulate reads: assuming that the monitoring
started at time t=0, when the system was described
by a Hilbert space vector 
, 
,
and when the monitoring
device was recording the logical value "no", the
probability 
that the change 
will
happen before time t is given by the formula:
where
and
Remark: The factor 
in the formula above is put
here for consistency with the notation used in our previous
papers.
It follows from the formula (1) that the probability
that the counter will be triggered out in the time interval (t,t+dt),
provided it was not triggered yet, is 
, where 
is
given by
We remark that 
is the probability that
the detector will notice the particle at all. In general this number
representing the total efficiency of the detector (for a given initial
state) will be smaller than 
