  With the approaching start-up of the experiments at LHC, the urgency to
quantify systematic uncertainties of the generators, used in the interpretation
of the data, is becoming pressing. The PHOTOS Monte Carlo program is often used
for the simulationof experimental, selection-sensitive, QED radiative
corrections in decays of Z bosons and other heavy resonances and particles.
Thanks to its complete phase-space coverage it is possible, with no
approximations for any decay channel, to implement the matrix-element. The
present paper will be devoted to those parts of the next-to-leading order
corrections for Z decays which are normally missing in PHOTOS. The analytical
form of the exact and truncated (standard) kernel used in PHOTOS will be
explicitly given. The correction, being the ratio of the exact to the
approximate kernel, can be activated as an optional contribution to the
internal weight of PHOTOS.
  To calculate the weight, the information on the effective Born-level Z/gamma*
couplings and even directions of the incoming beams, is needed. A universal
implementation would have made the PHOTOS solution less modular and less
convenient for the users. That is why, for the time being, we will keep the
correcting weight as an extra option, available for special tests only.
  We will quantify the numerical effect of the approximation with the help of a
multitude of distributions. The numerical size of the effect is in general
below 0.1%; however, in some corners of the phase-space (well defined and
contributing less than 0.5% to the total rate), it may reach up to about 20% of
their relative size.
