The "E" is for "Extreme." The EXPS3 offers true 2-eyes-open shooting and a 7 mm raised base that still allows for 1/3 iron sight co-witness. The EXPS3-2T Model denotes the 2 X 1 MOA Dots within the reticle surrounded by the 68 MOA ring. 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. Night vision-compatibility makes it a versatile choice for day or night hunting. Night vision capable for Gen I-III+ devices. Features Auto Shut Down at 8 hours.