A system for monitoring cardiac signals comprising: an electrode apparatus comprising a plurality of electrodes configured to be located proximate tissue of a patient; a display apparatus comprising a graphical user interface, wherein the graphical user interface is configured to present information for use in assisting a user in determining whether a signal is ambiguous; a computing apparatus coupled to the electrode apparatus and display apparatus; characterised in that the computing apparatus is configured to determine whether a signal acquired from a channel associated with an electrode is ambiguous, the computing apparatus configured to: i) calculate a first derivative of the signal; ii) determine a first minimum derivative and its corresponding first time index from the first derivative; iii) determine a second minimum derivative and its corresponding second time index within a window including the first minimum derivative and extending a pre-specified time period; iv) calculate a ratio of the first and second minimum derivatives; v) calculate a difference between the first time index and the second time index; and to determine based on the ratio of the first and second minimum derivatives and the difference between the first time index and the second time index whether the signal is ambiguous or non-ambiguous; and display on the display apparatus whether the signal is ambiguous or non-ambiguous. an electrode apparatus comprising a plurality of electrodes configured to be located proximate tissue of a patient; a display apparatus comprising a graphical user interface, wherein the graphical user interface is configured to present information for use in assisting a user in determining whether a signal is ambiguous; a computing apparatus coupled to the electrode apparatus and display apparatus; characterised in that the computing apparatus is configured to determine whether a signal acquired from a channel associated with an electrode is ambiguous, a display apparatus comprising a graphical user interface, wherein the graphical user interface is configured to present information for use in assisting a user in determining whether a signal is ambiguous; a computing apparatus coupled to the electrode apparatus and display apparatus; characterised in that the computing apparatus is configured to determine whether a signal acquired from a channel associated with an electrode is ambiguous, the computing apparatus configured to: i) calculate a first derivative of the signal; ii) determine a first minimum derivative and its corresponding first time index from the first derivative; iii) determine a second minimum derivative and its corresponding second time index within a window including the first minimum derivative and extending a pre-specified time period; iv) calculate a ratio of the first and second minimum derivatives; v) calculate a difference between the first time index and the second time index; and to determine based on the ratio of the first and second minimum derivatives and the difference between the first time index and the second time index whether the signal is ambiguous or non-ambiguous; and i) calculate a first derivative of the signal; ii) determine a first minimum derivative and its corresponding first time index from the first derivative; iii) determine a second minimum derivative and its corresponding second time index within a window including the first minimum derivative and extending a pre-specified time period; iv) calculate a ratio of the first and second minimum derivatives; v) calculate a difference between the first time index and the second time index; and to determine based on the ratio of the first and second minimum derivatives and the difference between the first time index and the second time index whether the signal is ambiguous or non-ambiguous; and display on the display apparatus whether the signal is ambiguous or non-ambiguous. <EOS>