A method of determining a filling level of a product contained in a tank using an intermittently operating level gauge system in which filling level determination events (10a-c) are separated by a time defining an update frequency, said method comprising, for each of said filling level determination events, the steps of: transmitting a first electromagnetic transmit signal towards a surface of said product; receiving a first electromagnetic echo signal resulting from reflection at at least one impedance transition encountered by said first electromagnetic transmit signal; determining a present echo characteristic value based on said first electromagnetic echo signal; and comparing said present echo characteristic value and a stored echo characteristic value, wherein said method further comprises the steps of: if a difference between said present echo characteristic value and said stored echo characteristic value is greater than a predefined value: transmitting at least a second electromagnetic transmit signal towards said surface; receiving at least a second electromagnetic echo signal resulting from reflection at at least one impedance transition encountered by said second electromagnetic transmit signal; and determining said filling level based on said at least second electromagnetic echo signal, if a difference between said present echo characteristic value and said stored echo characteristic value is less than said predefined value: determining said filling level based on stored data indicative of at least one previous filling level measurement; and storing an echo characteristic value indicative of the determined filling level. transmitting a first electromagnetic transmit signal towards a surface of said product; receiving a first electromagnetic echo signal resulting from reflection at at least one impedance transition encountered by said first electromagnetic transmit signal; determining a present echo characteristic value based on said first electromagnetic echo signal; and comparing said present echo characteristic value and a stored echo characteristic value, wherein said method further comprises the steps of: if a difference between said present echo characteristic value and said stored echo characteristic value is greater than a predefined value: transmitting at least a second electromagnetic transmit signal towards said surface; receiving at least a second electromagnetic echo signal resulting from reflection at at least one impedance transition encountered by said second electromagnetic transmit signal; and determining said filling level based on said at least second electromagnetic echo signal, if a difference between said present echo characteristic value and said stored echo characteristic value is less than said predefined value: determining said filling level based on stored data indicative of at least one previous filling level measurement; and storing an echo characteristic value indicative of the determined filling level. if a difference between said present echo characteristic value and said stored echo characteristic value is greater than a predefined value: transmitting at least a second electromagnetic transmit signal towards said surface; receiving at least a second electromagnetic echo signal resulting from reflection at at least one impedance transition encountered by said second electromagnetic transmit signal; and determining said filling level based on said at least second electromagnetic echo signal, transmitting at least a second electromagnetic transmit signal towards said surface; receiving at least a second electromagnetic echo signal resulting from reflection at at least one impedance transition encountered by said second electromagnetic transmit signal; and determining said filling level based on said at least second electromagnetic echo signal, if a difference between said present echo characteristic value and said stored echo characteristic value is less than said predefined value: determining said filling level based on stored data indicative of at least one previous filling level measurement; and storing an echo characteristic value indicative of the determined filling level. determining said filling level based on stored data indicative of at least one previous filling level measurement; and storing an echo characteristic value indicative of the determined filling level.