If a facility uses only aneroid instruments, the maximum discrepancy between two ASIs is

• A. 0.02
• B. 0.03
• C. 0.04
• D. 0.05

Answer: (D)

When you’re relying on only aneroid instruments for speed indication, the readings from two ASIs can drift a bit due to mechanical wear, temperature effects, and calibration tolerances. To keep readings believable and consistent in a training or test setup, the allowable difference between two ASIs is set at 0.05. This recognizes the inherent limitations of purely mechanical aneroid sensors while still preventing large mismatches that could mislead a pilot.

Smaller tolerances like 0.02, 0.03, or 0.04 would be stricter than what’s typically practical with aneroid-only instruments, making it harder to keep two indicators within spec as they age or heat up. If you observe a discrepancy larger than 0.05, it signals a need for calibration or servicing to restore consistency between indicators.