A flow-sensing arrangement within a spirometer. The arrangement includes a tubular-member for allowing an air-passage along a longitudinal-axis thereof. At-least two disc-shaped air-resistive elements are removably-arranged within the tubular member to resist the air-flow. Each of the resistive-elements include perforations for allowing the air-passage through the resistive-element. At-least two ports extend radially outward through a wall of the tubular member, such that each of the two ports are located within the tubular-member near the resistive-elements to cause determination of at least a pressure-difference there-between.
