A system comprising: one or more computers; and a computer-readable storage device having a computer program product encoded therein, the computer program product operable to cause the one or more computers to perform operations comprising: obtaining a first time varying physiological cardiac signal (310, 410, 510) and a second time varying physiological cardiac signal (310, 410, 510, 530) that relate to biological activity of an organism, the first time varying physiological cardiac signal (310, 410, 510) and the second time varying physiological cardiac signal (310, 410, 510, 530) forming an analytic pair wherein the analytic pair has a time varying phase angle; defining a reference line (453, 455) by a boundary of a representation of the time varying phase angle with respect to a time period; and identifying a fiducial point based on the reference line (453, 455), characterized in that the computer-readable storage device is further operable to cause the one or more computers to perform operations comprising: calculating a corresponding function (460, 560) to a downslope or an upslope of the representation of the time varying phase angle within the time period; and wherein identifying a fiducial point based on the reference line (453, 455) comprises identifying a fiducial point based on an intersection of the corresponding function (460, 560) and the reference line (453, 455). one or more computers; and a computer-readable storage device having a computer program product encoded therein, the computer program product operable to cause the one or more computers to perform operations comprising: obtaining a first time varying physiological cardiac signal (310, 410, 510) and a second time varying physiological cardiac signal (310, 410, 510, 530) that relate to biological activity of an organism, the first time varying physiological cardiac signal (310, 410, 510) and the second time varying physiological cardiac signal (310, 410, 510, 530) forming an analytic pair wherein the analytic pair has a time varying phase angle; defining a reference line (453, 455) by a boundary of a representation of the time varying phase angle with respect to a time period; and identifying a fiducial point based on the reference line (453, 455), obtaining a first time varying physiological cardiac signal (310, 410, 510) and a second time varying physiological cardiac signal (310, 410, 510, 530) that relate to biological activity of an organism, the first time varying physiological cardiac signal (310, 410, 510) and the second time varying physiological cardiac signal (310, 410, 510, 530) forming an analytic pair wherein the analytic pair has a time varying phase angle; defining a reference line (453, 455) by a boundary of a representation of the time varying phase angle with respect to a time period; and identifying a fiducial point based on the reference line (453, 455), characterized in that the computer-readable storage device is further operable to cause the one or more computers to perform operations comprising: calculating a corresponding function (460, 560) to a downslope or an upslope of the representation of the time varying phase angle within the time period; and wherein identifying a fiducial point based on the reference line (453, 455) comprises identifying a fiducial point based on an intersection of the corresponding function (460, 560) and the reference line (453, 455). calculating a corresponding function (460, 560) to a downslope or an upslope of the representation of the time varying phase angle within the time period; and wherein identifying a fiducial point based on the reference line (453, 455) comprises identifying a fiducial point based on an intersection of the corresponding function (460, 560) and the reference line (453, 455).