Which option correctly describes how to convey the altimeter setting to a Center when required?

• A. "QNH 29.92"
• B. "Local altimeter 29.92"
• C. "QNH 29.92 or Local altimeter 29.92, depending on context"
• D. "Altimeter 29.92"

Answer: (C)

Clear communication of the altimeter reference and its value is essential when talking to Center. Controllers need to know which pressure reference you’re using and the exact number so they can interpret your altitude correctly and maintain proper separation. Because practices vary by region and situation, you should convey either the QNH setting or the local altimeter setting, each with its numeric value. This ensures the Center understands exactly what altitude reference you are using—whether it’s station pressure adjusted to sea level (QNH) or the local field pressure (local altimeter). In some contexts you may use one or the other depending on the procedure or airspace, so stating the appropriate type and the value avoids ambiguity. For example, you might say you have QNH 29.92, or Local altimeter 29.92, depending on what applies in your area.