  We report on realization of 10 quantum Hall devices in series fabricated
using epitaxial graphene on silicon carbide. Precision measurements with a
resistance bridge indicates that the quantized Hall resistance across an array
at filling factor 2 is equivalent to 5 h/e^2 within the measurement uncertainty
of approximately 4 10-8. A quantum-Hall phase diagram for the array shows that
a metrological quantization of 5 h/e^2 can be achieved at the magnetic field of
6 T and temperature of 4 K. This experiment demonstrates the possibility of
timely unchangeable resistance reference in various ranges in relaxed
experimental conditions.
