A system for use in monitoring cardiac signals comprising: an electrode apparatus comprising a plurality of electrodes (2-14, n) configured to be located proximate tissue of a patient; 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 accurate onset data for depolarization of a heart; computing apparatus coupled to the electrode apparatus and display apparatus, characterized in that the computing apparatus is configured to: a)determine whether a signal acquired from a channel associated with an electrode from the plurality of electrodes is valid and sufficiently strong; b) eliminate one or more channels that acquire invalid signals; c) determine whether one or more remaining channels acquire sufficiently strong signals to allow onset data to be calculated; d) in response to determining one or more remaining channels acquire sufficiently strong signals: determine beat information including first local maximum for each beat; store the first local maximum for each beat into memory; determine whether a square of a first derivative of a signal is smaller than a preselected percentage of the first local maximum for the beat; and e) in response to determining whether a square of a first derivative is smaller than the preselected percentage of the first local maximum, update the onset data for the beat. an electrode apparatus comprising a plurality of electrodes (2-14, n) configured to be located proximate tissue of a patient; 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 accurate onset data for depolarization of a heart; computing apparatus coupled to the electrode apparatus and display apparatus, characterized in that the computing apparatus is configured to: a)determine whether a signal acquired from a channel associated with an electrode from the plurality of electrodes is valid and sufficiently strong; b) eliminate one or more channels that acquire invalid signals; c) determine whether one or more remaining channels acquire sufficiently strong signals to allow onset data to be calculated; d) in response to determining one or more remaining channels acquire sufficiently strong signals: determine beat information including first local maximum for each beat; store the first local maximum for each beat into memory; determine whether a square of a first derivative of a signal is smaller than a preselected percentage of the first local maximum for the beat; and e) in response to determining whether a square of a first derivative is smaller than the preselected percentage of the first local maximum, update the onset data for the beat. a)determine whether a signal acquired from a channel associated with an electrode from the plurality of electrodes is valid and sufficiently strong; b) eliminate one or more channels that acquire invalid signals; c) determine whether one or more remaining channels acquire sufficiently strong signals to allow onset data to be calculated; d) in response to determining one or more remaining channels acquire sufficiently strong signals: determine beat information including first local maximum for each beat; store the first local maximum for each beat into memory; determine whether a square of a first derivative of a signal is smaller than a preselected percentage of the first local maximum for the beat; and determine beat information including first local maximum for each beat; store the first local maximum for each beat into memory; determine whether a square of a first derivative of a signal is smaller than a preselected percentage of the first local maximum for the beat; and e) in response to determining whether a square of a first derivative is smaller than the preselected percentage of the first local maximum, update the onset data for the beat.