  We discuss the statistical and systematic uncertainties in the event
reconstruction (core location, and determination of S(1000), i.e., the signal
at a distance of 1000 m from the shower core) by the Pierre Auger surface
detector for showers with zenith angle less than 60 degrees. The method is
based on a maximum likelihood method where the reference lateral distribution
function is obtained through the experimental data. We also discuss S(1000) as
primary energy estimator.

Astrophysics