Signal processing systems for analysing data values obtained from a physical sensor arranged to give a digitised output indicative of the basal body temperature (BBT) of a female human user. The digitised output has a resolution of at least 0.01° Celsius and the method identifies at least one characteristic in a change in BBT for the user. The system includes a receiver for receiving a series of representative temperature values obtained for at least ten 24 hour periods, each value being derived from a set of at least 10 stabilised temperature readings obtained during a period of at least one hour. The series of representative temperature values is analysed to determine whether it includes a temperature change event indicative or predictive of ovulation and an ovulation indicator is generated. The values are further analysed to identify a timing for a temperature change event indicative or predictive of ovulation. The values are further analysed to determine whether the series meets a further predetermined criteria and a further indicator is generated. The ovulation indicator, the timing indicator and the at least one further indicator are processed to generate an output indicative of a physical state of the female human user.
