1. A pulse oximetry system for determining physiological information of a subject, comprising: a pulse oximetry sensor configured to generate an intensity signal, wherein the pulse oximetry sensor detects light attenuated by the subject; and a pulse oximeter coupled to the pulse oximetry sensor, wherein the pulse oximeter is configured to: determine a value indicative of a physiological rate of the subject; calculate a cross-correlation sequence based on a cross-correlation of the intensity signal and a reference waveform for a plurality of lags, wherein the cross-correlation sequence comprises a plurality of calculated cross-correlation values; select two segments from the cross-correlation sequence, wherein the two segments are the same size and each comprises a plurality of cross-correlation values, and wherein the starting points of the two segments are offset from each other; calculate one or more of: (a) distances based on the two segments and (b) angles based on the two segments; determine one or more metric values based on the calculated one or more distances and angles, wherein the one or more metric values indicate confidence as to whether the value indicative of the physiological rate of the subject is correct; determine whether to qualify the value indicative of the physiological rate of the subject based on the one or more metric values; determine a pulse rate value for the subject based on the value indicative of the physiological rate when the value indicative of the physiological rate is qualified; and display the pulse rate value for the subject on a display.