This allows you to dial back to your exact zero even after field adjustments. Lose the manual, and you might strip that tiny set screw using the wrong tool (often a 1.5mm or 2mm hex key, as noted in the manual).
Before mounting, adjust the eyepiece to ensure a sharp reticle. Point the scope at a neutral background (like a clear sky) and turn the fast-focus eyepiece until the reticle is crisp. Bushnell (RE3940BS9) Engage Rifle Scope -3-9X40 Illuminated Product Description. Renata 3 Volt 225mAh Li Coin. R&D Batteries 985-bushnell-legend-series-manual.pdf - Balistas.cz bushnell 3-9x40eg manual