An appraisal of the exercise electrocardiogram test. Part I-Applications, significance, and criticisms. GUBNER R. J Occup Med. 1960 Feb;2:57-61. PMID: 13829981
The "2-step" exercise electrocardiogram- a preliminary follow-up study of 200 cases. CHESKY K, PORDY L, MASTER AM. Bull N Y Acad Med. 1951 Jun;27(6):383. PMID: 14839373