START: normal breaths —>

tidal volume

Tidal volume: Volume of air entering the lungs
during NORMAL breathing.

expiratory reserve volume

Expiratory reserve volume: Volume of air that can be
forcefully exhaled from lungs AFTER a normal breath.

vital capacity

Vital capacity: Volume of air that can be exhaled
after taking the deepest breath possible.

inspiratory reserve volume

Inspiratory reserve volume: Volume of air that enters the
lungs during FORCED inspiration BEYOND the Tidal Volume.
Calculate by taking Vital Capacity and subtracting Tital Volume and Expiratory Reserve Volume; Inspiratory Reserve Volume is what is left.