THERMAL FLOWMETER

Disclosed is a thermal flowmeter for measuring mass flow of a medium in a measuring tube, comprising: a measuring tube having a tube wall and a tube axis; a sensor with four probes, extending from a sensor base into the measuring tube, wherein the probes are adapted to heat medium, to determine its temperature or to influence a flow of the medium; and an electronic circuit, adapted to operate the probes and to create and to provide flow measured values. Each probe has a probe base and a probe active portion, wherein the probe active portion is adapted to heat the medium, to determine the temperature of the medium, and/or to influence a flow of the medium. The probe bases define a rhombus on a surface of the sensor base, wherein the rhombus is defined by geometric centers of cross sections of the probe bases.