Note: I would advise a spirometer for measuring the capacity of the lungs.
The spirometer, a useful but rather expensive little instrument, measures accurately lung capacity.
Secure a spirometer and increase the lung capacity until it registers about two hundred and fifty cubic inches.
Hence, the spirometer directly measures the respiratory capacity, and only indirectly the pulmonary capacity.
The spirometer only registered 200 cubic inches instead of 260, which, according to Hutchinson's table, was his mean.
It will be found by occasional trials upon the spirometer that the breathing capacity increases with these exercises.
spirometer spi·rom·e·ter (spī-rŏm'ĭ-tər)
An instrument for measuring the volume of air entering and leaving the lungs.