  The quantum Hall effect (QHE) theoretically provides a universal standard of
electrical resistance in terms of the Planck constant $h$ and the electron
charge $e$. In graphene, the spacing between the lowest discrete energy levels
occupied by the charge carriers under magnetic field is exceptionally large.
This is promising for a quantum Hall resistance standard more practical in
graphene than in the GaAs/AlGaAs devices currently used in national metrology
institutes. Here, we demonstrate that large QHE devices, made of high quality
graphene grown by propane/hydrogen chemical vapour deposition on SiC
substrates, can surpass state-of-the-art GaAs/AlGaAs devices by considerable
margins in their required operational conditions. In particular, in the device
presented here, the Hall resistance is accurately quantized within $1\times
10^{-9}$ over a 10-T wide range of magnetic field with a remarkable lower bound
at 3.5 T, temperatures as high as 10 K, or measurement currents as high as 0.5
mA. These significantly enlarged and relaxed operational conditions, with a
very convenient compromise of 5 T, 5.1 K and 50 $\mu$A, set the superiority of
graphene for this application and for the new generation of versatile and
user-friendly quantum standards, compatible with a broader industrial use. We
also measured an agreement of the quantized Hall resistance in graphene and
GaAs/AlGaAs with an ultimate relative uncertainty of $8.2\times 10^{-11}$. This
supports the universality of the QHE and its theoretical relation to $h$ and
$e$, essential for the application in metrology, particularly in view of the
forthcoming Syst\`eme International d'unit\'es (SI) based on fundamental
constants of physics, including the redefinition of the kilogram in terms of
$h$.
