Systems, devices, methods, and techniques relating to the identification of fiducial points. In one aspect, a machine implemented method includes obtaining a first time varying physiological signal and a second time varying physiological signal that relate to biological activity of an organism, the first time varying physiological signal and the second time varying physiological signal forming an analytic pair wherein the analytic pair has a time varying phase angle, defining a reference line by a lower 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.
