  A new method of momentum measurement of charged particles through Multiple
Coulomb Scattering (MCS) in the OPERA lead emulsion target is presented. It is
based on precise measurements of track angular deviations performed thanks to
the very high resolution of nuclear emulsions. The algorithm has been tested
with Monte Carlo (MC) pions. The results are found to describe within the
expected uncertainties the data obtained from test beams. We also report a
comparison of muon momenta evaluated through MCS in the OPERA lead emulsion
target with those determined by the electronic detectors for neutrino charged
current interaction events. The two independent measurements agree within the
experimental uncertainties, and the results validate the algorithm developed
for the emulsion detector of OPERA.
