Adevice that uses the wet/dry bulb method to measure the the sling psychrometer. as seen here, two thermometers are attached to a handle or length of rope and then are spun around in the air for a few minutes.

relative humidity

Explanation:

In general, a psychrometer is an instrument composed of two thermometers, used to measure the relative humidity of the air with high precision. As seen in the question above, the two thermometers allow a simultaneous measurement of the temperatures of the wet bulb and the dry bulb. Meteorologists usually use a more efficient form of the psychrometer to measure relative humidity, which is the sling psychrometer.

the real answer is b. scintillation counter

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