Which instrument is used to measure rainfall?

Correct answer: Rain gauge

Direct answer: Option D is correct. A rain gauge is the instrument used to measure rainfall. It collects rain falling into a container, and the collected water is measured, commonly in millimetres. A reading of 1 millimetre means that, if the water were spread evenly over a flat surface, it would form a layer 1 millimetre deep. The instrument must be placed in a suitable open position so buildings, trees, or walls do not block rainfall or add splashing. Option D works because a rain gauge is specifically designed to measure the amount of precipitation. Option A, the thermometer, measures temperature, not rainfall. Option B, the barometer, measures atmospheric pressure. Option C, the compass, shows direction, usually with reference to north, but it does not measure weather elements such as rainfall. Thus the instrument must be matched with the element it measures. Memory cue: rain means rain gauge; temperature means thermometer; pressure means barometer; direction means compass.