A volume unit (VU) meter or standard volume indicator (SVI) is a device displaying a representation of the signal level in audio equipment. The Acoustical Society of America standardized it in 1942 (C16-5 - 1942) for use in telephone installation and radio broadcast stations. Consumer audio equipment often features VU meters, both for utilitarian purposes (e.g. in recording equipment) and for aesthetics (in playback devices).

The original VU meter is a passive electromechanical device, namely a 200 µA DC d'Arsonval movement ammeter fed from a full wave copper-oxide rectifier mounted within the meter case. The mass of the needle causes a relatively slow response, which in effect integrates the signal, with a rise time of 300 ms. 0 VU is equal to +4 [dBu], or 1.228 volts RMS across a 600 ohm load, or about 2.5 milliWatts. 0 VU is often referred to as "0 dB". The meter was designed not to measure the signal, but to let users aim the signal level to a target level of 0 VU (sometimes labelled 100%), so it is not important that the device is non-linear and imprecise for low levels. In effect, the scale ranges from −20 VU to +3 VU, with −3 VU right in the middle. Purely electronic devices may emulate the response of the needle; they are VU-meters inasmuch as they respect the standard.

The metre, or meter (American spelling), (from the Greek noun μέτρον, "measure") is the base unit of length in the International System of Units (SI). The SI unit symbol is m. The metre is defined as the distance travelled by light in a specific fraction (1/299 792 458) of a second.

The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. In 1889, it was redefined in terms of a prototype metre bar (the actual bar used was subsequently changed twice). In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. In 1983, the current definition was adopted.

The imperial inch is defined as 0.0254 metres (2.54 centimetres or 25.4 millimetres). One metre is about 3 ³⁄₈ inches longer than a yard, i.e. about 39 ³⁄₈ inches.

Spelling

Metre is the standard spelling of the metric unit for length in all English-speaking nations except the USA, which uses meter.

Measuring devices (such as ammeter, speedometer) are spelled "-meter" in all countries. The word "meter", signifying any such device, has the same derivation as the word "metre", denoting the unit of length.

A hymn meter or metre indicates the number of syllables for the lines in each stanza of a hymn. This provides a means of marrying the hymn's text with an appropriate hymn tune for singing.

Hymn and poetic meter

In the English language poetic meters and hymn meters have different starting points but there is nevertheless much overlap. Take the opening lines of the hymn Amazing Grace:

Analyzing this, a poet would see a couplet with four iambic metrical feet in the first line and three in the second. A musician would more likely count eight syllables in the first line and six in the second.

Completing that verse:

the hymnist describes it as 8.6.8.6 (or 86.86).

Conventionally most hymns in this 86.86 pattern are iambic (weak-strong syllable pairs). By contrast most hymns in an 87.87 pattern are trochaic, with strong-weak syllable pairs:

In practice many hymns conform to one of a relatively small number of meters (syllable patterns), and within the most commonly used ones there is a general convention as to whether its stress pattern is iambic or trochaic (or perhaps dactylic). It is rare to find any significant metrical substitution in a well-written hymn; indeed, such variation usually indicates a poorly constructed text.

A measuring instrument is a device for measuring a physical quantity. In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item under study and the referenced unit of measurement. Measuring instruments, and formal test methods which define the instrument's use, are the means by which these relations of numbers are obtained. All measuring instruments are subject to varying degrees of instrument error and measurement uncertainty.

Scientists, engineers and other humans use a vast range of instruments to perform their measurements. These instruments may range from simple objects such as rulers and stopwatches to electron microscopes and particle accelerators. Virtual instrumentation is widely used in the development of modern measuring instruments.