An apparatus for sensing a biopotential signal on the skin of a person using at least a first skin electrode, a second skin electrode and a reference skin electrode for spaced placement on said skin of said person, the apparatus comprising: - a first terminal for connection to said first electrode, - a second terminal for connection to said second electrode, - a first circuitry configured for measuring the biopotential signal from said first and said second terminal, - a third terminal for connection to said reference skin electrode, - a first variable controlled resistance load connected to said first terminal, - a second variable controlled resistance load connected to said second terminal, - a first signal generator for generating a first alternating signal connected to said first terminal, - a second signal generator for generating a second alternating signal connected to said second terminal, - a fourth circuitry connected to the output of said first circuitry and configured to apply a variable controlled gain to the output signal of said first circuitry, - a controller in receipt of: • an output signal of said first circuitry, • a signal comprising a component representative of the amplitude of said first alternating signal, • a signal comprising a component representative of the amplitude of said second alternating signal, the controller being configured: • to determine the amplitude of said first alternating signal, • to determine the amplitude of said second alternating signal, • to control said first variable controlled resistance load and said second variable controlled resistance load, • to control said variable controlled gain, • to adapt the load of said first variable controlled resistance load as a function of a change in the determined amplitude of said first alternating signal, • to adapt the load of said second variable controlled resistance load as a function of a change in the determined amplitude of said second alternating signal, and • to adjust said variable controlled gain as a function of the determined amplitude of said first alternating signal and of the determined amplitude of said second alternating signal, when, and only when, the determined amplitude of both said first alternating signal and said second alternating signal change simultaneously. - a first terminal for connection to said first electrode, - a second terminal for connection to said second electrode, - a first circuitry configured for measuring the biopotential signal from said first and said second terminal, - a third terminal for connection to said reference skin electrode, - a first variable controlled resistance load connected to said first terminal, - a second variable controlled resistance load connected to said second terminal, - a first signal generator for generating a first alternating signal connected to said first terminal, - a second signal generator for generating a second alternating signal connected to said second terminal, - a fourth circuitry connected to the output of said first circuitry and configured to apply a variable controlled gain to the output signal of said first circuitry, - a controller in receipt of: • an output signal of said first circuitry, • a signal comprising a component representative of the amplitude of said first alternating signal, • a signal comprising a component representative of the amplitude of said second alternating signal, the controller being configured: • to determine the amplitude of said first alternating signal, • to determine the amplitude of said second alternating signal, • to control said first variable controlled resistance load and said second variable controlled resistance load, • to control said variable controlled gain, • to adapt the load of said first variable controlled resistance load as a function of a change in the determined amplitude of said first alternating signal, • to adapt the load of said second variable controlled resistance load as a function of a change in the determined amplitude of said second alternating signal, and • to adjust said variable controlled gain as a function of the determined amplitude of said first alternating signal and of the determined amplitude of said second alternating signal, when, and only when, the determined amplitude of both said first alternating signal and said second alternating signal change simultaneously. • an output signal of said first circuitry, • a signal comprising a component representative of the amplitude of said first alternating signal, • a signal comprising a component representative of the amplitude of said second alternating signal, • to determine the amplitude of said first alternating signal, • to determine the amplitude of said second alternating signal, • to control said first variable controlled resistance load and said second variable controlled resistance load, • to control said variable controlled gain, • to adapt the load of said first variable controlled resistance load as a function of a change in the determined amplitude of said first alternating signal, • to adapt the load of said second variable controlled resistance load as a function of a change in the determined amplitude of said second alternating signal, and • to adjust said variable controlled gain as a function of the determined amplitude of said first alternating signal and of the determined amplitude of said second alternating signal, when, and only when, the determined amplitude of both said first alternating signal and said second alternating signal change simultaneously.