  Series connection of four quantum Hall effect (QHE) devices based on
epitaxial graphene films was studied for realization of a quantum resistance
standard with an up-scaled value. The tested devices showed quantum Hall
plateaux RH,2 at filling factor i = 2 starting from relatively low magnetic
field (between 4 T and 5 T) when temperature was 1.5 K. Precision measurements
of quantized Hall resistance of four QHE devices connected by triple series
connections and external bonding wires were done at B = 7 T and T = 1.5 K using
a commercial precision resistance bridge with 50 microA current through the QHE
device. The results showed that the deviation of the quantized Hall resistance
of the series connection of four graphene-based QHE devices from the expected
value of 4*RH,2 = 2h/e^2 was smaller than the relative standard uncertainty of
the measurement (< 1*10^-7) limited by the used resistance bridge.
