There is disclosed a method of measuring at least one time-varying signal emission from the contents of a receptacle while the contents are subject to repeated cycles of temperature variations within a thermal cycling range, the method comprising: measuring the signal emission from the contents of the receptacle at repeating intervals of time and recording the signal emission measurement and a time stamp at each interval; recording a time stamp for each temperature of the thermal cycling range; and synchronizing the signal emission to a specific temperature within the thermal cycling range by comparing time stamps of the signal emission measurements to a time stamp for each temperature of the thermal cycling range.