A cassette module for a differential flowmeter has a first channel and a second channel which carry fluid during operation of the differential flowmeter and are permeated by a magnetic field during operation of the differential flowmeter, each having an electrode pair arranged on the first channel and on the second channel. A flow difference between the first fluid-carrying channel and the second fluid-carrying channel can be determined by comparing the signals on the first electrode pair and on the second electrode pair. The first channel has an additional section that is permeated by the magnetic field during operation. Another electrode pair is arranged in the additional section, so that a change in the measurement conditions can be detected by comparing the signal on the first electrode pair and on the additional electrode pair.