Ohuhu Red Dot Sight Rifle Scope with Free 20mm Mount Rails Black Red/green dual illumination & clear 4.0 MOA dot - Optimal brightness settings allow the shooter to find the perfect brightness needed for the environment, lighting, and weather conditions at hand. (Totally 10 brightness settings, manually adjusted) Quick-aim electronic dot sight - two eyes open method of sighting, which greatly enhances situational awareness and target acquisition speed Anti-reflective and band pass coated lens provides superior light transmission, resolution and scratch-resistance This scope fits onto any Weaver-style rail system or Picatinny 1913 mounting system thanks to an integrated mounting clamp Runs on 1 CR2032 battery (included) - 2,000 hours of battery life on low setting.