  We predict conductance oscillations in a quantum-anomalous Hall 2d strip
having a superconducting region of length $L_x$ with a chiral Majorana mode.
These oscillations require a finite transverse extension of the strip $L_y$ of
a few microns or less. Measuring the conductance periodicity with $L_x$ and a
fixed bias, or with bias and a fixed $L_x$, yields the speed of the chiral
Majorana mode. The physical mechanism behind the oscillations is the
interference between backscattered chiral modes from second to first interface
of the NSN double junction. The interferometer effect is enhanced by the
presence of side barriers.
