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A rain gauge measures precipitation collected over a known horizontal area. The reported rainfall depth is collected liquid volume divided by collector area: $h=V/A$. A tipping-bucket gauge converts repeated fixed-volume tips into accumulated depth; a weighing gauge measures collected mass.

Wind can deflect drops around the opening, and evaporation, splashing or freezing can bias the result. A gauge samples one location, so its reading need not represent a whole catchment during spatially uneven rain. The instrument geometry and exposure are therefore part of interpreting the observation.

A weather station is a set of instruments measuring atmospheric conditions at a specified site. A thermometer records temperature, a barometer records pressure, an anemometer records wind, and a rain gauge measures collected rainfall. Moisture observations may be reported as relative humidity or dew point.

Instrument exposure is part of the measurement. Direct sunlight can heat a temperature sensor above the surrounding air; nearby buildings alter wind; the height and averaging interval affect comparability. A long record therefore needs instrument and site metadata as well as numbers. Consistent observations support both immediate meteorology and the statistics used in climatology.