  The OPERA experiment, designed to conclusively prove the existence of $\rm
\nu_\mu \to \nu_\tau$ oscillations in the atmospheric sector, makes use of a
massive lead-nuclear emulsion target to observe the appearance of $\rm
\nu_\tau$'s in the CNGS $\rm \nu_\mu$ beam. The location and analysis of the
neutrino interactions in quasi real-time required the development of fast
computer-controlled microscopes able to reconstruct particle tracks with
sub-micron precision and high efficiency at a speed of 20 cm^2 / h. This paper
describes the performance in particle track reconstruction of the European
Scanning System, a novel automatic microscope for the measurement of emulsion
films developed for OPERA.
