A gas meter comprising: a channel (156; 256; 356; 656; 756) comprising a modifiable channel portion (158; 358; 658; 758) with a modifiable cross-sectional area, wherein the cross-sectional area of the modifiable channel portion (158; 358; 658; 758) is modifiable by adjusting the position of a plunger to control the velocity through the modifiable channel portion (158; 358; 658; 758) for a given flow rate; and a thermal mass flow meter positioned within the modifiable channel portion and which measures the mass flow rate by heating a portion of the flowing fluid and then recording how that heat is dispersed by the flow; wherein the gas meter is further characterized in that the gas meter is configured to operate in four states, the four states comprising: a first state in which the plunger is fully down, and the thermal mass flow meter is in a calorimeter sensor mode; a second state in which the plunger is fully down, and the thermal mass flow meter is in a Constant Temperature Anemometer sensor mode; a third state in which the plunger is fully up, and the thermal mass flow meter is in the calorimeter sensor mode; and a fourth state in which the plunger is fully up, and the thermal mass flow meter is in the Constant Temperature Anemometer sensor mode, wherein the fully up and fully down positions of the plunger are defined by the range of motion of the plunger within the modifiable channel portion, and wherein the modifiable channel portion is configured to permit fluid flow in all of the four states. a channel (156; 256; 356; 656; 756) comprising a modifiable channel portion (158; 358; 658; 758) with a modifiable cross-sectional area, wherein the cross-sectional area of the modifiable channel portion (158; 358; 658; 758) is modifiable by adjusting the position of a plunger to control the velocity through the modifiable channel portion (158; 358; 658; 758) for a given flow rate; and a thermal mass flow meter positioned within the modifiable channel portion and which measures the mass flow rate by heating a portion of the flowing fluid and then recording how that heat is dispersed by the flow; wherein the gas meter is further characterized in that the gas meter is configured to operate in four states, the four states comprising: a first state in which the plunger is fully down, and the thermal mass flow meter is in a calorimeter sensor mode; a second state in which the plunger is fully down, and the thermal mass flow meter is in a Constant Temperature Anemometer sensor mode; a third state in which the plunger is fully up, and the thermal mass flow meter is in the calorimeter sensor mode; and a fourth state in which the plunger is fully up, and the thermal mass flow meter is in the Constant Temperature Anemometer sensor mode, a first state in which the plunger is fully down, and the thermal mass flow meter is in a calorimeter sensor mode; a second state in which the plunger is fully down, and the thermal mass flow meter is in a Constant Temperature Anemometer sensor mode; a third state in which the plunger is fully up, and the thermal mass flow meter is in the calorimeter sensor mode; and a fourth state in which the plunger is fully up, and the thermal mass flow meter is in the Constant Temperature Anemometer sensor mode, wherein the fully up and fully down positions of the plunger are defined by the range of motion of the plunger within the modifiable channel portion, and wherein the modifiable channel portion is configured to permit fluid flow in all of the four states.