  Experimental results of the absolute air-fluorescence yield are given very
often in different units (photons/MeV or photons/m) and for different
wavelength intervals. In this work we present a comparison of available results
normalized to its value in photons/MeV for the 337 nm band at 1013 hPa and 293
K. The conversion of photons/m to photons/MeV requires an accurate
determination of the energy deposited by the electrons in the field of view of
the experimental set-up. We have calculated the energy deposition for each
experiment by means of a detailed Monte Carlo simulation and the results have
been compared with those assumed or calculated by the authors. As a result,
corrections to the reported fluorescence yields are proposed. These corrections
improve the compatibility between measurements in such a way that a reliable
average value with uncertainty at the level of 5% is obtained.
