The correct choice is (c) Time Measurements
To explain I would say: Time measurements and heart rate measurements are made horizontally on the electrocardiogram. Electrocardiograms are almost invariably recorded on graph paper with horizontal and vertical lines at 1 mm intervals with a thicker line at 5 mm intervals. Amplitude measurements are made vertically in millivolts. The sensitivity of an electrocardiograph is typically set at 10 mm/mV.
