  The accuracy of measuring the total energy of the spectators in the FHCal
calorimeter, depending on the fluctuations in the number of nucleons and the
hadron shower is obtained. It is shown that, from the point of view of
statistics, the process of registering photoelectrons in a photomultiplier (PM)
is similar to the process of registering spectator nucleons in a calorimeter.
The measurements of single photoelectrons in the PM are in good agreement with
the obtained formula for the relative variance of the charge detected by the
PM.
