Thermal flow meter for measuring the mass flow, in particular of a gaseous medium, in a measuring tube, comprising: a measuring tube with a measuring tube wall (11.1); a sensor with four probes (12.2), wherein the probes extend into the measuring tube starting from a sensor base body (12.1) and wherein the probes are configured to heat up the medium, determine its temperature or influence a flow of the medium in the measuring tube; an electronic measuring/operating circuit that is configured to operate at least three probes, as well as to both prepare and make available the flow readings attained through their operation, wherein each probe exhibits one probe base body and one active probe body, wherein the probe base body is arranged on a side of the corresponding probe facing the sensor base body and wherein the active probe body is arranged on a side of the corresponding probe facing away from the sensor base body, wherein the active probe body is configured to heat up the medium, determine the temperature of the medium and/or influence a flow of the medium in the measuring tube, wherein the probe base bodies feature a column-shaped design, wherein the probe base bodies are spread out on a surface of the sensor base body in a rhombus shape, wherein the rhombus is defined by centroid points of cross-sections of the probe base body and exhibits both a first diagonal and a second diagonal, wherein a first probe (12.21) is configured to measure the temperature of the medium, wherein a second probe (12.22) and a third probe (12.23) are configured to heat up the medium and each determine their own temperature, wherein the first probe is arranged on a first side of the first diagonal and wherein the third probe is arranged on a second side of the first diagonal, wherein the second probe and a fourth probe (12.24) are arranged on opposing sides of the second diagonal, wherein a first diagonal of the rhombus shape exhibits a rotation angle η to a standard (11.3) of a measuring tube cross-section (11.2), wherein η is greater than 1 degree, in particular greater than 2 degrees and preferably greater than 3 degrees, characterized in that the fourth probe is configured to restrict a partial flow of the medium between the first probe and the third probe, wherein the active probe body of the fourth probe (12.24) exhibits a first width parallel to the first diagonal and a second width parallel to the second diagonal, wherein the second width is greater than the first width by a factor of at least 1.1, in particular at least 1.2 and preferably at least 1.3, and wherein a centroid of the active probe body of the fourth probe is offset in the direction of the second probe. a measuring tube with a measuring tube wall (11.1); a sensor with four probes (12.2), wherein the probes extend into the measuring tube starting from a sensor base body (12.1) and wherein the probes are configured to heat up the medium, determine its temperature or influence a flow of the medium in the measuring tube; an electronic measuring/operating circuit that is configured to operate at least three probes, as well as to both prepare and make available the flow readings attained through their operation, wherein each probe exhibits one probe base body and one active probe body, wherein the probe base body is arranged on a side of the corresponding probe facing the sensor base body and wherein the active probe body is arranged on a side of the corresponding probe facing away from the sensor base body, wherein the active probe body is configured to heat up the medium, determine the temperature of the medium and/or influence a flow of the medium in the measuring tube, wherein the probe base bodies feature a column-shaped design, wherein the probe base bodies are spread out on a surface of the sensor base body in a rhombus shape, wherein the rhombus is defined by centroid points of cross-sections of the probe base body and exhibits both a first diagonal and a second diagonal, wherein a first probe (12.21) is configured to measure the temperature of the medium, wherein a second probe (12.22) and a third probe (12.23) are configured to heat up the medium and each determine their own temperature, wherein the first probe is arranged on a first side of the first diagonal and wherein the third probe is arranged on a second side of the first diagonal, wherein the second probe and a fourth probe (12.24) are arranged on opposing sides of the second diagonal, wherein a first diagonal of the rhombus shape exhibits a rotation angle η to a standard (11.3) of a measuring tube cross-section (11.2), wherein η is greater than 1 degree, in particular greater than 2 degrees and preferably greater than 3 degrees, characterized in that the fourth probe is configured to restrict a partial flow of the medium between the first probe and the third probe, wherein the active probe body of the fourth probe (12.24) exhibits a first width parallel to the first diagonal and a second width parallel to the second diagonal, wherein the second width is greater than the first width by a factor of at least 1.1, in particular at least 1.2 and preferably at least 1.3, and wherein a centroid of the active probe body of the fourth probe is offset in the direction of the second probe.