THERMAL FLOWMETER

A thermal flowmeter for measuring the mass flow rate of a medium in a measuring tube, includes: a measuring tube having a measuring tube wall; a sensor having four probes that project into the measuring tube from a main sensor body; and an electronic measuring/operating circuit designed to operate at least three probes and to generate and provide flow measurement values by operating the probes, each probe having a main probe body and an active probe body, the active probe body designed to heat the medium, to determine the temperature of the medium and/or to influence a flow of the medium in the measuring tube, wherein the main probe bodies span a rhombus on a surface of the main sensor body, and the rhombus is defined by centroid points of cross-sections of the main probe bodies.