q.1) Willem Einthoven created the electrocardiogram in the early 1900s after studying the mechanisms of electromagnetism and Waller's capillary electrometer.
q.2) The electrocardiogram created by Einthoven was only available for upper classes.
q.3) Among positive aspects of an electrocardiogram are following factors: it is a simple diagnostic procedure, painless and safe for humans, it does not require preparation, it can be carried out repeatedly without restrictions, it does not bring discomfort to the patient.
Among negative aspects of an electrocardiogram are following factors: accuracy of diagnosis depends on the qualification of the doctor, this diagnostic method is short-term, it can only fix pathology with a stable electrocardiographic pattern. Also, the cardiogram does not display cardiac hemodynamics, it cannot be used to determine the presence of heart murmurs. The electrocardiogram cannot identify defects with tumors.