1. An apparatus for selecting output physiological parameter values, the apparatus comprising: one or more processors configured to: receive an input physiological signal; receive values of a physiological parameter derived from the input physiological signal, and select output physiological parameter values by at least adjusting between smoothing the physiological parameter values and tracking the physiological parameter values; wherein said adjusting is performed based at least in part on one or more characteristics of the input physiological signal, the one or more characteristics comprising one or more of the following: signal confidence in the input physiological signal and a desired time lag.