The ERA-TAC ACI Angle Cosine Indicator (MPN: T0941-0000) is a passive, mechanical instrument manufactured by RECKNAGEL in Germany. Engineered for precision rifles, it calculates the cosine of uphill or downhill inclination angles to determine gravity-equivalent horizontal distance. When aiming on an incline, an internal damped pendulum aligns with gravity to display the cosine factor via a red indicator line. Multiplying this factor by the direct line-of-sight range yields the adjusted horizontal distance required for turret elevation adjustments. Built to withstand high-recoil platforms including .338 Lapua Magnum and .50 BMG, the unit mounts alongside the optic at axis height using the ERA-TAC Universal Interface system.

Key Features

• Passive Gravity-Driven Operation: Operates entirely via an internal damped pendulum mechanism that requires 0V and zero battery power.
• Direct Cosine Readout: Displays the cosine of the angle directly on the dial (such as 0.87 for a 30° slope) to allow rapid multiplication against line-of-sight range.
• ERA-TAC Universal Interface Integration: Designed to mount to compatible ERA-TAC brackets (such as the T0940 series with bubble level) to keep turrets and left-side illumination controls unobstructed.
• Recoil-Proof Mechanical Integrity: Calibre-rated by the manufacturer to handle severe recoil forces, including heavy tactical magnums up to .50 BMG.

Product Specifications

• Manufacturer: RECKNAGEL GmbH & Co. KG (ERA-TAC)
• Manufacturer Part Number (MPN): T0941-0000
• Operating Power: 0V (mechanical pendulum; no batteries required)
• Weight: Approximately 30 g distributor package specification (shipping weight up to 50 g)
• Packaged Dimensions: Approximately 120 mm (L) × 90 mm (W) × 90 mm (H)
• Mount Compatibility: ERA-TAC Universal Interface (requires T0940 adapter bracket series, sold separately)
• Recoil Rating: 100% recoil-proof across all standard and magnum calibres (.338 Lapua Magnum, .50 BMG)

Who is the Era-Tac Aci Angle Cosine Indicator for?

• Long-range precision rifle competitors shooting in mountainous terrain — benefits from a scope angle cosine indicator operating at 0V with no batteries that can fail during high-angle stages, providing an instantaneous mechanical cosine multiplier directly alongside the optic axis.
• Mountain hunters engaging targets at extreme elevation angles — relies on a 30 g mechanical indicator to calculate gravity-corrected horizontal shot distance without adding substantial weight to an alpine rifle setup.

Less suitable for: Shooters operating across flat terrain, engaging targets at close ranges under 150 m where angle adjustments are negligible, or targeting distances beyond 400 m where bullet drag and aeroflight demand raw degree inputs fed into an electronic ballistic solver rather than manual cosine multiplication.