What is the annual wedge transmission factor constancy tolerance?

• A. ±1%
• B. ±3%
• C. ±2%
• D. ±4%

Answer: (C)

The annual wedge transmission factor constancy tolerance is about how much the wedge’s light transmission can change from one year to the next while still being considered stable. The transmission factor is the fraction of light that passes through the wedge, and even a well-made wedge can drift slightly over time due to aging, coating changes, contamination, or environmental effects. Setting a tolerance defines how much drift is acceptable before you need to recheck or re-calibrate.

Two percent is the typical balance: it’s small enough to keep calibration accurate but not so tight that minor aging trips every year. If the baseline transmission factor is, say, 0.90, the acceptable yearly variation would keep it within roughly 0.882 to 0.918. Choosing a larger tolerance (like four percent) would risk noticeable calibration shifts; a smaller one (like one percent) could be impractical to maintain with normal aging. Therefore, the best choice is a ±2% tolerance.