In general, any object that reflects incident energy. Usually it is a device designed for specific reflection characteristics.

The writing component of a recording instrument.

See evaporative opportunity.

The ratio of the existing amount of water vapor in the air at a given temperature to the maximum amount that could exist at that temperature. Usually expressed in percent.

The closeness of agreement among a number of consecutive output values measuring the same input value under the same operating conditions, approaching from the same direction. Usually measured as nonrepeatability but expressed as repeatability, a percenta ...

The closeness of agreement among measurements of the same value of the same quantity where the individual measurements are made under different defined conditions, i.e. by different methods or with different measuring instruments.

A type of electrical thermometer in which the thermal element is a substance whose electrical resistance varies with the temperature. Such thermometers can be made with very short time constants and are capable of highly accurate measurements.

The smallest change in the environment that causes detectable change in the indication of an instrument. Compare to sensitivity.

The value of the quantity measured, as indicated or otherwise provided by a measuring instrument.

The time required for an instrument to register a designated percentage (frequently 90%) of a step change in the variable being measured.

A defective maximum thermometer of the liquid-inglass type in which the mercury flows too freely through the constriction. Such a thermometer will indicate a maximum temperature that is too low.

A mercury-in-glass thermometer which records the temperature upon being inverted and retains its reading until being returned to the first position.

Abbreviation for radio frequency.

An elongated area of relatively high pressure. Usually associated with and most clearly identified as an area of maximum anticyclonic curvature of the wind flow. The opposite of a trough.

An accumulation of granular ice tufts on the windward sides of exposed objects that is formed from supercooled fog or cloud and built out directly against the wind.

The total area drained by a river and its tributaries. Same as watershed.

A forecast of the expected stage or discharge at a specified time, or of the total volume of flow within a specified Interval of time, at one or more points along a stream.

A device for measuring the river stage. Also called stream gauge.

See stage.

Root Mean Square. This notation is used frequently with error analysis. In that context, it is the square root of the arithmetic mean of the squares of the deviations of the individual calibration points from the theoretical or ideal response.