Amulets of eternal combat are though to have been created long ago by the followers of a war god during an age of savage violence. 

Every 10th round of combat, one quarter of the hit points you have lost since the last activation of the amulet are restored to you. This does not include any healing and subsequent hit point loss--simply subtract your current hit points from the total you had 10 rounds ago, and divide by 4 (rounding up). You gain these points back at the beginning of the round.