La Marzocco LINEA MINI Manual Del Usuario página 26

It is possible to regulate the pressure of the steam boiler by
12
pressure switch.
26
This parameter is set at the factory at a preset nominal temperature.
11
The temperature of the brewing water is measured at the most
critical point in the integrated brew group where temperature
fluctuation is the greatest.
The temperature of the water exiting the group head is held
constant by means of the mass of the group casting. Even though
the temperature of the water may vary slightly, the temperature of
the water exiting the group is constant.
To properly calibrate the temperature of any espresso machine it is
import to measure the temperature of the water exiting the group by
means of an external temperature measuring device.