the jump of the critical current with the $n$ change at $\Phi = (n+0.5) \Phi _{0}$ not only of the double contour interferometer but also, for example, of a superconducting ring with asymmetric link-up of current leads. A simple magnetometer based on the latter prediction was proposed in [@Letter2014]. But measurements of aluminium ring with asymmetric link-up of current leads have revealed that a smooth change of its critical current is observed at $\Phi \approx (n+0.5) \Phi _{0}$ instead of the jump which must be observed due to the change of the quantum number from $n$ to $n+1$ [@PLA2017]. Our observations of the voltage jumps up to $V _{max} - V _{min} \approx 20 \ \mu V$, Fig.3, and higher mean that the derivative $(\partial \overline{V}/\partial \Phi _{e}) _{I}$ can reach high values when the voltage $\overline{V}$ average in the time $\Theta \gg 1/f$ changes from $\overline{V} \approx V _{min}$ to $\overline{V} \approx V_{max}$ in the narrow interval $\Delta \Phi \approx \Phi _{0}/\epsilon \ll \Phi _{0}/2$: for example $(\partial \overline{V}/\partial \Phi _{e}) _{I}  \approx (V _{max} - V _{min})/\Delta \Phi \approx  20 \ mV/\Phi _{0}$ at $V _{max} - V _{min} \approx 20 \ \mu V$ and the real value 