quantum number of the bottom loop should be equal permanently zero $n _{d} = 0$ whereas the quantum number the upper loop may change from $n _{u} =0$ to $n _{u} =1$ (or from $n _{u} =1$ to $n _{u} = 0$) after successive switching of the loop segment in the normal state by the short pulse of the external current $I_{sw}$, Fig.1. The probability of the minimum value of the voltage $V _{min}$ (the maximum value of the critical current $I _{c,DD} = 2 I _{c,j}$ ) should be equal the probability (3) of the state $n _{u} =0$ because $n _{u} + n _{d} = 0 + 0 = 0$ is even. Therefore the voltage average in the time $\overline{V} = \Theta ^{-1}\int _{\Theta} dt V(t) \approx V _{min}P(n _{u} =0) + V _{max}P(n _{u} =1)$ should change from the minimum value $\overline{V} \approx V _{min}$ to the maximum value $\overline{V} \approx V_{max}$ in the narrow interval $\Delta \Phi \approx \Phi _{0}/\epsilon \ll \Phi _{0}/2$ at $\epsilon \gg 1$. The DDCI may be more sensitive than the conventional dc SQUID due to this sharpness of the voltage $\overline{V}$ change at its most sensitive point $\Phi \approx 0.5 \Phi 