The "E" is for "Extreme." The EXPS3 offers true 2-eyes-open shooting and a 7 mm raised base that still allows for iron sight access. It features easy-to-adjust side buttons and an adjustable, locking, quick-detach lever for easy attachment and removal. Its night vision-compatibility makes it a versatile choice for day or night hunting.An operator-grade Holographic Weapon Sight built for close-quarter engagements with fast-moving targets, our Model EXPS3 HWS delivers two eyes open shooting, 7mm raised base for lower iron sight access, and night vision capability. Side buttons and an adjustable, quick-detach locking lever for easy installation and removal. t is also the optic of choice for the technologically advanced modern rifle hunter. Its night vision-compatibility makes it a versatile choice for day or night hunting. Feature: 20 daylight settings brightness 10 additional settings for Gen I through III+ night vision devices 1000 continuous hours battery life at nominal setting 12 at room temperature Water-resistant -33 feet depth