Figure 4: Bland-Altman plots between heart rates measured by the electrocardiogram and those measured by the smartphone using the six algorithms for selection of region of interest. Note that two subjects were excluded for the FCR algorithm; namely, the number of subjects was 48 for the FCR algorithm and 50 for the other algorithms. VAR: variance; SER: spectral energy ratio; TM: template matching; TD: temporal difference; GRAD: gradient; FCR: fixed central region; HR: heart rate; bpm: beat per minute.