EKG strips are strips of paper that display visual readouts from an electrocardiogram (EKG or ECG). They are divided into several small squares, each measuring one millimeter and representing 0.04 seconds. Thicker lines form a larger grid with five squares on each side, representing an interval of 0.2 seconds. Vertical columns represent one mV of voltage for every ten squares. Heart rate is displayed in a staggered line along the grid. They are usually fed into an EKG machine and rolled out during printing.