Chief among these differences is the ability to see color and the ability to see in low light. To understand the differences it is important to understand how the human eye works and from that a derivative can be made to other mammalian species. The eye itself is composed of various components.
If each small box is equal to 0.04 seconds or 1 mm, then the standard ECG speed is 1 mm per 0.04 seconds or 25 mm per second. The standard approach to reading an ECG includes in this order: 1  Examining the rate.  Examining the rhythm.
The normal PR interval is from 120 ms to 200 ms in length. This is measured from the initial deflection of the P wave to the beginning of the QRS complex. In first-degree heart block, the diseased AV node conducts the electrical activity more slowly.