HRT Tables are used to translate the externally read voltages of the sensor inputs into values that are then used within the ECU in their normal form. 


For example, below we can see the TPS HRT. This converts the voltage read from the chosen analog voltage channel (by assinging to that channel TPS Raw) to a 'useful' value, the Throttle Position (TPS) in percent.


Essentially, HRTs allow external sensors to be calibrated anyway the tuner wishes. The standard layout for the common four sensors (IAT, Coolant, TPS and MAP) as well as a selection of the digital readouts are pre-laid out in the "Sensor Cals" tab of MEITE if using a Default Layout.