Abstract: A computing circuit is disclosed for producing a digital representation of the ratio between a reference analog signal and successive analog signals that are successively supplied to a single input of the computing circuit. The computing circuit comprises storage means in which a digital representation of the reference analog signal is retained. For each successive analog signal that is supplied to the input of the computing circuit, a digital output is generated that is commensurate with the values of the supplied successive analog signal and the digital representation of the reference analog signal retained in the storage means. The digital output is displayed in numerical form representing the ratio between the reference analog signal and the successive analog signal.