It looks to the that pitottube has a bit of a misunderstanding, if not then my answer is not needed.
Jet engines are flat rated to a certain teperature, in the case of CFM-56 it is ISA+15°C or 30°C on a standard day.
What this means is that the engine is capable of giving out full thrust up to that temperature, but if it gets hotter than that, it will give out less thrust (due to less denisty and less energy we can put into the air before reaching the ITT (inlet turbine temperature) maximum limit).
Therefore, if we don't require the maximum engine thrust for T/O, then we tell the engine that it is hotter than it actually is, the engine knows that at this high (assumed) temperature it can not give us the full engine thrust, reduces the thrust accordingly.
Less thrust=lower RPM=lower temperature in the core=less strain on the engine=more engine life.
One last note though. If one whishes to use use assumed temp reduction, one must always use temperature that is higher than the flat rated temp on the engines, otherwise it will still give us full thrust.
Regards Fresca