This is fortunately a one off question and basically refers to the input to and the output from the computer.

The command signal is initially passed to the comparitor, which then compares it to the current position of the aircraft before feeding a signal (epsilon) to the computer.

The computer then determines the required control deflection (betaC) to satisfy the input.

The piloting law is thus based on the control surface movement required (betaC) to achieve a desired change of attitude (epsilon) .