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HowMany - Unit Dictionar Category: Mathematics and statistics > Dictionary of unit measurements Date & country: 26/09/2008, USA Words: 1293

nibble
a unit of information used in computer science. A nibble is 4 bits or 1/2 byte. The cuter spelling nybble, suggested by byte, is sometimes used. In different contexts, a group of 4 bits is sometimes called a quadbit or a hexit.

nile
a unit used in nuclear engineering to describe the 'reactivity' of a nuclear reactor. One nile is a reactivity of 0.01 or 1%. Since this is a rather large amount, reactivity is measured for practical purposes in milliniles, with one millinile = 10^-5. The nile was invented in the British nuclear power industry. For a discussio...

nip
an informal unit of liquid volume. The term 'nip' often means 'a small amount,' with no precise equivalent. In U.S. bartending, a nip is often taken to be 2 fluid ounces (about 59 milliliters). In Britain, a nip of spirits is considered to be 1/6 gill (about 22.95 milliliters or 0.776 U.S. fluid ounce); a nip of beer is 1/4 pint (the same as a gill...

Nm or N•m
symbol for newton meter, a unit of torque (see above).

Nm
abbrevation for normal metric, a symbol for the density of worsted yarns. Yarn is described as a/b Nm if it is a-ply (has a individual strands) and there are b kilometers of yarn per kilogram. An example might be 2/40 Nw, describing a 2-ply yarn having 40 kilometers per kilogram. If the yarn is single-ply, the a is often omitted, so a single-ply ya...

noeud
French word for the knot (1.852 km/h) the traditional unit of velocity at sea. This non-metric unit is still used officially in France; for example, Meteo France uses it in maritime weather forecasts.

nonet
a unit of quantity equal to 9, used mostly in music to describe an ensemble of 9 instruments.

nook
a traditional unit of land area in northern England. Originally the nook was 1/2 virgate; a virgate, often called a yardland in the north, was about 30 acres in southern England but tended to be closer to 40 acres in the north. A nook of land thus came to be 20 acres or about 8.094 hectares.

normal (N)
a term used in chemistry to describe a solution having a concentration of 1 gram equivalent per liter. The normal concentration of an ion is effectively equal to the molar concentration divided by the valence (the number of free or missing electrons) of the ion.

normal cubic meter (Nm3)
a unit of mass for gases equal to the mass of 1 cubic meter (35.3147 ft³) at a pressure of 1 atmosphere and at a standard temperature, often 0 °C (32 °F) or 20 °C (68 °F). The term standard cubic meter is also used; sometimes both are used, with different temperatures. Because industry practice varies, the...

normal liter (NL or Nl or Ndm3)
a unit of mass for gases equal to the mass of 1 liter (0.035 3147 ft³) at a pressure of 1 atmosphere and at a standard temperature, often 0 °C (32 °F) or 20 °C (68 °F). Air flow is often stated in normal liters per minute (Nl/min).

nose
an informal unit of length, equal to roughly half the length of a horse's head, used in expressing the results of a horse race.

note
a unit of relative time in music, also called a whole note, equal to 1/2 breve.

noy
a unit of perceived noisiness introduced by the American acoustics engineer K. D. Kryter in 1959. An observer uses the unit to described the noise levels he or she experiences as multiples of a standard level. The standard level, one noy, is defined to be the noisiness of a random noise signal within the frequency band from 910 to 1090 hertz at a s...

nu
a measure of the dispersiveness (or constringence, as it is called) of a lens or prism. If b, y, and r are the indices of refraction at blue, yellow, and red wavelengths, respectively, then the nu value is (y - 1)/(b - r). The measure is represented by the Greek letter nu, and sometimes the symbol 'nu' is used as if it were a unit, as in 65 nu.

Nw
symbol for normal worsted, a unit measuring the density of worsted yarns. Worsted yarn is described as a/b Nw if it is a-ply (has a individual strands) and there are b 560-yard hanks of yarn per pound. An example might be 2/40 Nw, describing a 2-ply yarn having 40 hanks (22 400 yards) per pound. If the yarn is single-ply, the a is often omitted, so...

nybble
see nibble, above.

octad
a unit of quantity equal to 8.

octarius
an obsolete name for the British Imperial pint (34.678 cubic inches or approximately 568.261 milliliters), used in British medicine and pharmacy during the nineteenth century. The octarius was equal to 1/8 congius (gallon).

octennium
a unit of time equal to 8 years.

octet
a unit of quantity equal to 8. The name comes from the Latin numeral octo.

octet
a unit of information equal to 8 bits, used primarily in telecommunications. In most contexts, this is the same as a byte, but the byte can sometimes vary in size while the octet is always exactly 8 bits.

octuple, octuplet
a group of 8 items, especially 8 identical items; the word octuplet is also used for one member of the group.

odds
a statement of the probabilities that an event will or will not happen. If an event has a-b (or a to b, or a:b) odds in its favor, then the probability is being divided into a + b parts; the probability is a/(a + b) that the event will happen and b/(a + b) that it will not happen. In sports, however, the odds quoted are often odds that a contestant...

Oechsle
see degree Oechsle.

oersted (Oe)
another name for the gauss as a unit of magnetic flux density.

ogdoad
another name for an octad; this very learned spelling is a transliteration of the ancient Greek.

ohm
a traditional German unit of liquid volume, no longer in use. The ohm, spelled aume in English, was generally equal to 1/6 fuder or roughly 150 liters (40 U.S. gallons).

ohm meter
a unit of resistivity, measuring the extent to which a substance offers resistance to passage of an electric current. The resistivity of a conductor in ohm meters is defined to be its resistance (in ohms) multiplied by its cross-sectional area (in square meters) divided by its length (in meters).

oka or oke
a traditional unit of weight in Turkey and throughout the eastern Mediterranean. The oka is approximately 2.8 pounds or 1.28 kilograms, although its size varied somewhat over the large area formerly included in the Turkish empire. In Greece, the oka was standardized at 1282 grams and remained in use until traditional units were prohibited in 1959. ...

omer
a ancient unit of volume for grains and dry commodities, used in the Bible. The omer was equal to 0.1 ephah; this is believed to equal about 4.032 liters, 246.05 cubic inches, 0.9154 U.S.dry gallon, or 0.8869 British imperial gallon.

omn. bih.
traditional abbreviation for the Latin omni bihorio, once every two hours, a unit of frequency sometimes used in medical prescriptions. The abbreviation alt. h. (alternis horis, every other hour) is equivalent.

omn. hor.
traditional abbreviation for the Latin omni hora, once every hour, a unit of frequency sometimes used in medical prescriptions. The abbreviation q. h. (quaque hora, each hour) is equivalent.

onça, once, oncia, onza
traditional names for the ounce unit in Romance languages. The Portuguese onça and Spanish onza equal 1/16 libra or about 28.69 grams (1.012 ounce); the French once equals 1/16 livre or about 30.59 grams (1.079 ounce). The Italian oncia or onza is no longer used, but traditionally it equaled 1/12 libra or about 27.3 grams (0.96 ounce).

ons
a Dutch unit of weight or mass, now used as a metric unit equal to the hectogram (100 grams, or about 3.5274 ounces).

open window unit (owu)
the original name of the unit of sound absorption now called the sabin.

osmolal, osmolar
notations used by chemists to describe the concentration of ions in chemical solutions. The term 'osmolal' describes an ion concentration of a solution in moles per kilogram of solvent (mol/kg), while 'osmolar' describes an ion concentration in moles per liter (mol/L).

ostent
a medieval name for the time unit now called the minute. (In medieval times a minute was equal to 1/10 hour, or 6 modern minutes). The ostent was equal to 8 ounces (see below).

ounce
an old term for a 1/12 part, the English equivalent of the Latin uncia (see def. above). In medieval times, the word was used sometimes for a unit of distance equal to 1/12 yard or 3 inches. It was also used for a unit of time equal to 1/12 moment, or 7.5 seconds. In some settings, an ounce of time was divided into exactly 47 atoms.

ounce force (ozf or oz)
a traditional unit of force, equal to the force experienced at the earth's surface by a mass of one ounce. One ounce force equals 1/16 pound force or about 0.278 014 newton.

ounce mole (ozmol)
a unit of amount of substance. One ounce mole of a chemical compound is the same number of ounces as the molecular weight of a molecule of that compound measured in atomic mass units. Thus the ounce mole is equal to 28.349 52 moles.

ounce per gallon (oz/gal)
a traditional unit of mass concentration. One ounce per U.S. gallon equals 7.489 152 grams per liter (g/L). In Britain, 1 ounce per imperial gallon is equal to 6.236 023 grams per liter.

ounce per square foot (oz/ft2)
a traditional unit of density, still used widely in the U.S. for stating the density of coatings, the 'weight' of leather, the rates of application for lawn chemicals, and many other applications. One ounce per square foot is equal to 0.305 152 kilogram per square meter (kg/m²).

ounce weight (oz)
a traditional unit for measuring the density (incorrectly called the 'weight') of a fabric. In most cases, the stated ounce density of a fabric is its density in ounces per square yard (oz/yd²). 1 ounce per square yard is equal to 33.9057 grams per square meter (g/m² or gsm). However, when the fabric is...

oxgang
an old English unit of land area equal to 1/8 hide or roughly 15 acres (6 hectares). The hide was considered the area a farmer could plow with a team of 8 oxen, so an oxgang was the area he could plow with a single ox. The unit was also called the bovate, from the Latin word bos for an ox or cow.

pace
in military use, the term 'pace' is often used as an alternate name for the step; see military pace.

pack (pk)
a commercial unit specifying the number of items per package. In retail trade, packages containing 4 items (for example) are often described as '4 pack' or '4pk.' The symbol pk is also used for the peck (see below).

packen
a traditional Russian unit of weight equal to 1200 funte, 30 pudi (see pud below), 1083 pounds, or 491.4 kilograms.

pair royal
a unit of quantity equal to 3, used in cribbage to describe three cards of the same rank. This usage recalls the original meaning of 'pair' as a group of equivalent objects, not necessarily two in number. Four cards of the same rank form a 'double pair royal.'

palm
a traditional unit of distance equal to the length of a person's hand, from the wrist to the end of the middle finger. In the English system this unit is equal to 9 inches (22.86 centimeters) and is usually called a span. The confusion between the two palm units is ancient. In Roman times, the longer unit was known as the palmus major and the short...

palm
a name sometimes used in Dutch for the decimeter (10 centimeters, or about 3.937 inches).

Paris foot
an English name for the French royal foot (pied de roi, see below).

part
a unit used in informal statements of proportion or in prescriptions for mixtures. The fraction of an ingredient present is the number of parts of that ingredient divided by the total number of parts present. For example, hummingbirds can be attracted to feeders with a mixture of 1 part sugar dissolved in 4 parts water (equivalent to a solution of ...

part
a medieval unit of time equal to 1/15 hour or 4 minutes.

particle flux unit (pfu)
a unit used to measure the rate at which energetic particles, such as protons, are received by spacecraft. These flux rates are a major component of the 'space weather,' the environment in which satellites and other spacecraft operate. One pfu is a rate of one particle per square centimeter of detector area per steradian of solid angle scanned per ...

part per quadrillion (ppq)
a unit of proportion equal to 10^-15.

part per thousand (ppth or ppt)
a unit of proportion equal to 0.001, also called per mill (see below).

pascal second (Pa•s)
the SI unit of dynamic viscosity, equal to 10 poise or 1000 centipoise. Some scientists propose calling this unit the poiseuille (Pl), but that name has not been accepted by the General Conference on Weights and Measures.

pcf, pci
symbols for pound per cubic foot or per cubic inch, traditional engineering units of density. 1 pcf = 16.018 46 kg/m³ and 1 pci = 1728 pcf = 27 679.90 kg/m³.

pebi- (Pi-)
a binary prefix meaning 2⁵⁰ = 1 125 899 906 842 624. This prefix, adopted by the International Electrotechnical Commission in 1998, is supposed to replace peta- for binary applications in computer science. The prefix is a contraction of 'petabinary.'

pentad
a unit of quantity equal to 5.

pentad
a unit of time equal to 5 days. This unit is common in meteorology, where forecasts are frequently made for periods of 5 days at a time.

per annum (PA)
a traditional unit of frequency equal to once a year.

perch
a unit of area equal to one square perch . A perch of area covers exactly 272.25 square feet or about 25.292 85 square meters. There are 40 perches in a rood and 160 perches in an acre.

perch
a traditional unit of volume for stone and other masonry. A perch of masonry is the volume of a stone wall one perch (16.5 feet) long, 18 inches high, and 12 inches thick. This is equivalent to exactly 24.75 cubic feet, 0.916 667 cubic yard, or about 0.700 842 cubic meter.

perch
a traditional unit of distance in Ireland standardized at 21 English feet (6.4008 meters) or 14/11 English perch or rod. Since the Irish perch was 27.27% longer than the English, the Irish chain, furlong, and mile were longer in the same proportion..

perche or perch
a traditional unit of area in French North America, equal to one square perche . A perche of area is therefore equal to 0.01 arpent, about 368.007 square feet (40.8896 square yards) or 34.189 square meters.

per diem (PD)
a traditional unit of frequency equal to once a day.

perfect ream
see printer's ream (below).

perm
a traditional unit of water vapor permeability, that is, the ability of a material to permit the passage of water vapor. If we want to keep things dry, we wrap them in something having low permeability. A material has a permeability of one perm if it allows transmission of one grain of water vapor per square foot of area per inch of mercury (inHg) ...

per mensem
a traditional unit of frequency equal to once a month.

perm inch
a traditional unit of water vapor permeance. The perm value (see above) does not depend on the thickness of the material used as a water barrier. The permeance is the product of the perm value and the thickness, measured in inches. One perm inch equals about 1.453 x 10^-12 kg/(m•Pa•s) at 0 °C or about 1.459 x 10...

person hour
a gender-nonspecific version of man hour, a unit of labor equal to the work of one person for one hour.

perthousand
another name for per mill (see above). In typography, 'perthousand' is often used as the name of the per mill character.

pes
the Roman foot, equal to 29.67 centimeters (about 11.68 inches). The pes was divided into 12 unciae (inches). There were 5 pes (or pedes) in 1 passus (pace, see above), 10 in a decempeda, 625 in a stadium, and 5000 in the Roman mile.

petabecquerel (PBq)
a unit of radioactivity equal to 10¹⁵ atomic disintegrations per second or 27 027.03 curies.

petaflops (Pflops)
a unit of computing power equal to one quadrillion (10¹⁵) floating point operations per second. See flops. Current computers cannot achieve this power; it is a goal for future generations of supercomputers.

petagram (Pg)
a metric unit of mass equal to 10¹⁵ grams or 1 gigatonne (one billion metric tons). This unit is used in atmospheric science and other scientific contexts where large masses are considered.

petahertz (PHz)
a unit of frequency equal to 10¹⁵ hertz. The frequencies of infrared and visible light waves are expressed in petahertz.

petajoule (PJ)
a metric unit of energy. One petajoule equals 947.817 billion Btu, 277.7778 gigawatt hours, or about 9.48 megatherms.

petameter (Pm)
a metric unit of distance equal to 10¹² kilometers. This is equivalent to about 621.371 billion miles or 0.1057 light year. The distance from the earth to the nearest star (other than the sun) is about 40 petameters.

pF
symbol for the picofarad.

pF
a unit formerly used in agricultural science to measure 'soil suction' or soil moisture tension. Soil moisture tension is the pressure that must be applied to the moisture in the soil to bring it to hydraulic equilibrium with an external pool of water. This was measured in pF units as the logarithm of the pressure in centimeters of water. Currently...

pferdestärke (PS)
German word for horsepower, meaning the metric horsepower. The symbol ps is used for horsepower in both the Japanese and German automotive industies.

pfu
symbol for the particle flux unit (see above).

photon
a quantum of light energy, or, more generally, of any form of electromagnetic energy having a single wavelength, direction, and polarization.

photon
a former name for the unit of retinal illuminance now called the troland.

pi
a very famous mathematical unit. The circumference of a circle is equal to pi multiplied by the diameter, so pi is equal to the ratio between the circumference and diameter of a circle, any circle. It turns out that pi is an irrational number, which means that its decimal expansion is nonterminating and nonrepeating. To 25 significant digits, pi eq...

pic
see pik, below.

picocurie (pCi)
a common unit of radioactivity, used to measure radioactivity occurring naturally in the environment. One picocurie equals 10^-12 curie or 0.037 becquerel; this corresponds to one atomic disintegration about every 27 seconds--a very low rate of activity.

picofarad (pF)
a common unit of electric capacitance equal to 10^-12 farad. This unit was formerly called the micromicrofarad (µµF).

picogram (pg)
a metric unit of mass equal to 10^-12 gram or one millionth of a microgram.

picoliter (pl or pL)
a metric unit of volume equal to 10^-12 liter or 1000 cubic micrometers. Engineers at Eastman Kodak recently reported a technique for producing ink droplets as small as several picoliters.

picolo
a unit of volume for champagne, equal to 1/4 bottle (187.5 milliliters).

picomole (pmol)
a unit of amount of substance equal to 10^-12 mole. This unit is common in biochemistry; since a mole of a large organic molecule can be quite a large amount, a picomole is larger than one might think.

picosecond (ps)
a unit of time equal to 10^-12 second.

picotesla (pT)
a unit of magnetic field strength equal to 10^-12 tesla or 10^-8 gauss.

picul
a unit of weight comparable to the European quintal, widely used in East Asia during the colonial period. The picul is equal to 100 catties, typically about 133.3 pounds or 60.5 kilograms. In recent years the picul has been used as a metric unit equal to 60 kilograms (132.28 pounds) in Thailand or 50 kilograms (110.23 pounds) in China. The unit is ...

pie
the traditional foot of Spain. The pie equals 1/3 vara or 12 pulgadas (see below). The pie used in Spain is about 27.86 centimeters or 10.97 inches, but in Spanish Latin America the pie is generally longer. The Argentine length is 28.89 centimeters or 11.37 inches; in Texas, 1/3 vara is 11 1/9 inches or 28.22 centimeters.

pieze (pz)
a metric unit of pressure, part of the 'metre-tonne-second' system sometimes used by European engineers. The pieze is a pressure of one sthene per square meter, or 1000 newtons per square meter, or one kilopascal. This is not such a large pressure; one pieze equals 10 millibars or about 0.145 pound per square inch. The name of the unit comes from t...