Meteorology · Instruments — Psychrometer
A sling (or aspirated) psychrometer measures humidity by comparing:
- AThe dry-bulb and wet-bulb temperatures, from which dewpoint and relative humidity are derived✓ Correct
- BWind speed and direction
- CPressure and altitude
- DSea and air temperature only
Explanation
A psychrometer has a dry-bulb thermometer and a wet-bulb (wrapped in a wet wick). Evaporative cooling lowers the wet-bulb reading; the difference (wet-bulb depression) is used with tables to find dewpoint and relative humidity — key for anticipating fog and assessing comfort/cargo conditions.
Authority: WMO; Bowditch (Pub. No. 9)
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