[whereswaldo]

The bottom arrow is a ratio of player health vs target health. If you have 100% health and your target has 60% health, then the bottom arrow would be halfway between the center of the bar and the left side of the bar. If you are at equal health, it would be right in the middle. If your target has more health than you it would move to the right of center. And lastly, if one of you is dead, it would be all the way to the left or right, depending on who is dead.