A method of smoothing a perfusion index measurement, said method being performed by an oximeter system and comprising the following steps: receiving intensity signal data responsive to intensity signals acquired from a detector capable of detecting light attenuated by body tissue; calculating a current value of perfusion index and inputting said current value into a smoother module, said smoother module further accepting one or more indicators of the quality of the intensity signal data and performing the following steps: when said one or more indicators indicate a good quality of the received intensity signal data, a baseline perfusion index becomes the current value of perfusion index and the baseline perfusion index is output, and when said one or more indicators indicate a poor quality of the received intensity signal data, the current value of the perfusion index is compared to the baseline perfusion index, and when said current value of perfusion index is smaller than the baseline perfusion index, the baseline perfusion index becomes the current value of perfusion index and the baseline perfusion index is output, and when said current value of perfusion index is greater than or equal to the baseline perfusion index, the baseline perfusion index is output. receiving intensity signal data responsive to intensity signals acquired from a detector capable of detecting light attenuated by body tissue; calculating a current value of perfusion index and inputting said current value into a smoother module, said smoother module further accepting one or more indicators of the quality of the intensity signal data and performing the following steps: when said one or more indicators indicate a good quality of the received intensity signal data, a baseline perfusion index becomes the current value of perfusion index and the baseline perfusion index is output, and when said one or more indicators indicate a poor quality of the received intensity signal data, the current value of the perfusion index is compared to the baseline perfusion index, and when said current value of perfusion index is smaller than the baseline perfusion index, the baseline perfusion index becomes the current value of perfusion index and the baseline perfusion index is output, and when said current value of perfusion index is greater than or equal to the baseline perfusion index, the baseline perfusion index is output. when said one or more indicators indicate a good quality of the received intensity signal data, a baseline perfusion index becomes the current value of perfusion index and the baseline perfusion index is output, and when said one or more indicators indicate a poor quality of the received intensity signal data, the current value of the perfusion index is compared to the baseline perfusion index, and when said current value of perfusion index is smaller than the baseline perfusion index, the baseline perfusion index becomes the current value of perfusion index and the baseline perfusion index is output, and when said current value of perfusion index is greater than or equal to the baseline perfusion index, the baseline perfusion index is output. when said current value of perfusion index is smaller than the baseline perfusion index, the baseline perfusion index becomes the current value of perfusion index and the baseline perfusion index is output, and when said current value of perfusion index is greater than or equal to the baseline perfusion index, the baseline perfusion index is output.