From: A manual for physical measurements for use in normal schools: public and preparatory schools, boys’ clubs, girls’ clubs, and young men’s Christian associations, with anthropometric tables for each height of each age and sex from five to twenty years, and vitality coefficients, by William Walter Hastings, Phd.  Published by the International Young Men’s Christian Association Training School, 1901. page 18.

“The pupil, after loosening the clothing about the chest and taking a full inspiration, filling the lungs completely, should blow steadily into the spirometer until all the air possible has been expelled from the lungs.  Two or three trials may be allowed.”