For most measurement setups, the sound wave will need to travel through several different materials, and the measured ToF is the sum of the ToF through each component. In order to isolate the ToF of one component of a measurement setup, two approaches can be taken. One is to measure the thicknesses of each component and use known speeds of sound whenever possible (e.g. for water when used as a coupling fluid) in order to calculate the portion of the ToF due to the component of interest. Another possibility is to combine measurement modes: a combination of transmission and pulse-echo measurements, for example, can be used to isolate the ToF of a sample from the ToF due to surrounding coupling fluid. The method is explained in more detail later.