  The absolute value of the air-fluorescence yield is a key parameter for the
energy reconstruction of extensive air showers registered by fluorescence
telescopes. In previous publications, we reported a detailed Monte Carlo
simulation of the air-fluorescence generation that allowed the theoretical
evaluation of this parameter. This simulation has been upgraded in the present
work. As a result, we determined an updated absolute value of the fluorescence
yield of 7.9+-2.0 ph/MeV for the band at 337 nm in dry air at 800 hPa and 293
K, in agreement with experimental values. We have also performed a critical
analysis of available absolute measurements of the fluorescence yield with the
assistance of our simulation. Corrections have been applied to some
measurements to account for a bias in the evaluation of the energy deposition.
Possible effects of other experimental aspects have also been discussed. From
this analysis, we determined an average fluorescence yield of 7.04+-0.24 ph/MeV
at the above conditions.

Instrumentation and Methods for Astrophysics