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daily value (DV)
a unit of nutrition used in the United States. The U.S. Food and Drug Administration establishes recommended daily amounts of various nutrients, both "good" ones like vitamins and "bad" ones like fat and sodium. These so-called daily values are based on a hypothetical person, male or female, who requires a diet of 2000 Calories per day. The results are approximate at best, since nutritional needs vary with age, sex, and other factors. Food packages generally carry nutritional lables specifying the amount of each nutrient contained in a standard serving, expressed as a percentage of the daily value (%DV).
dalton (Da or D)
an alternate name for the unified atomic mass unit (u or amu).
a traditional Chinese weight unit, previously spelled tan in many English works. During the European colonial era the unit was equal to 100 catties or 133.333 pounds. In modern China the dan is equal to 100 jin, which is exactly 50 kilograms (110.231 pounds). The dan is the Chinese equivalent of the European quintal or hundredweight.
data mile
a unit of distance used in radar technology. The data mile equals exactly 6000 ft or 1828.8 meters; this is equivalent to about 1.137 statute (ordinary) miles or 0.9875 nautical miles. U.S. military radar equipment is often calibrated in data miles.
deadweight ton (dwt)
a traditional unit of weight or mass used in the shipping industry. The deadweight tonnage of a ship is the difference between its weight when completely empty and its weight when fully loaded. This includes the weight of everything portable carried by the ship: the cargo, fuel, supplies, crew, and passengers. The deadweight ton is traditionally equal to the British ("long") ton of 2240 pounds (1016.047 kilograms). However, more often it is being taken to equal the metric ton (1000 kilograms, or 2204.623 pounds).
deca- (da-)
a metric prefix meaning 10, derived from the Latin word for ten, decem. The Greek form deka- is also used, and it has the advantage of avoiding confusion with deci-, one tenth. The International Bureau of Weights and Measures (BIPM) specifies deca- for the prefix and da- for the symbol. In its interpretation of the International System (SI) for U.S. use, the U.S. National Institute of Standards and Technology (NIST) recommends deka- for the spelling of the prefix. Following NIST, this dictionary uses the spelling deka-.
a traditional unit of quantity equal to 10. Also called the decad. 10 years, 10 days or 1/3 month. In medieval English this unit was anglicized as the dicker.
the number 10 million (107).
a unit of time equal to 10 years; another name for a decade. The census in the U.S. is called decennial because it is taken every ten years.
deci- (d-)
a metric prefix meaning one tenth, or 0.1. The prefix is derived from the Latin word decimus for a tenth.
decibar (dbar)
a metric unit of pressure equal to 0.1 bar or 10 kilopascals. One decibar equals 75.006 torr, or 1.450 pounds per square inch (lbf/in2 or psi). The decibar is often used to measure the pressure of seawater, because an increase of 1 decibar in pressure corresponds closely to an increase of 1 meter in depth.
decibel (dB)
a customary logarithmic measure most commonly used (in various ways) for measuring sound. The human ear is capable of detecting an enormous range of sound intensities.  Experiment shows that when humans perceive one sound to be twice as loud as another, in fact the louder sound is about ten times as intense as the fainter one. For this reason, sound is measured on logarithmic scales. Informally, if one sound is 1 bel (10 decibels) "louder" than another, this means the louder sound is 10 times louder than the fainter one. A difference of 20 decibels corresponds to an increase of 10 x 10 or 100 times in intensity.

For sound intensity (the power of the sound waves per unit of area) 0 decibels is equal 1 picowatt per square meter; this corresponds approximately to the faintest sound that can be detected by a person who has good hearing. A quiet room has a normal sound intensity of around 40 decibels, ten thousand times louder than the faintest perceptible sound, and a thunderclap may have an intensity of 120 decibels, a trillion times louder than the faintest sound.
decigram (dg)
a metric unit of mass equal to 100 milligrams or about 1.5432 grains.
a statistical unit equal to 10 percentiles, or 1/10 of a ranked sample.
deciliter (dl or dL)
a common metric unit of volume equal to 0.1 liter or 100 cubic centimeters. A deciliter contains 6.10237 cubic inches, 3.38140 U.S. fluid ounces, or 3.519 British fluid ounces. The deciliter is similar in size to the gill, an old English unit of volume.
decimeter (dm)
a fairly common metric unit of distance equal to 10 centimeters or 3.9370 inches. The decimeter is very close to the hand, a traditional English unit.
decimillimeter (dmm)
a metric unit of distance equal to 0.1 millimeter (10-4 meter) or about 3.937 mils. The use of compound prefixes such as decimilli- is not permitted in the SI.
an empirical unit of indoor odor intensity introduced by the Danish environmental scientist P.O. Fanger in 1988.
decitex (dtex)
a common metric unit of yarn density equal to 0.1 tex, 0.9 denier (see below), or 0.1 milligram per meter. This unit was previously called the drex.
decitonne (dt or dtn)
a metric unit of mass or weight equal to 100 kilograms (220.4623 pounds). This unit is becoming common in international trade; it is the same as the Russian centner, the German doppelzentner, and the French metric quintal.
degree (° or deg)
the standard unit of angle measure, equal to 1/360 circle, 60 minutes, 3600 seconds, or about 0.017 453 293 radian. So far as we know, this unit was introduced by the Greek geometer Hipparchus of Nicaea (125 BC), who developed the first trigonometric tables.

A unit of distance sometimes used at sea, equal to 60 nautical miles, approximately 69.05 statute miles, or 111.12 kilometers. This distance is the average length of one degree of latitude. Because the Earth is not exactly spherical, a degree of latitude actually varies from about 68.7 miles at the Equator to 69.4 miles at the poles. One degree of longitude is about 69.17 miles at the Equator.

Any of the various units of temperature. In the U.S., the unmodified unit "degree" generally means the degree Fahrenheit; in other countries, it means the degree Celsius.

A unit measuring the hardness of water. Water is called "hard" if it contains a high concentration of mineral salts, especially calcium carbonate. This concentration can be expressed clearly in parts per million (ppm) or in milligrams per liter (mg/L).

Various scientific quantities, especially specific gravity and viscosity, have been measured in "degrees" based on the readings of particular instruments. The degree scales of Baumé (see below) and Beck, and many others, have been used in measuring specific gravity, and the scales of Engler and MacMichael are common in the measurement of viscosity.

The percentage of alcohol, by volume, present in a mixture. In winemaking, for example, a 13° wine is 13% alcohol by volume (13% v/v), also called the degree Gay-Lussac (° GL) after the French chemist Joseph-Louis Gay-Lussac (1778-1850).

A unit used in mathematics to describe algebraic expressions. The degree of an expression having a single variable is the highest exponent (or power) to which that variable appears. If the expression has more than one variable, then the degree is the highest total exponent of the individual terms, where in each term the exponents of the different variables are added. Thus x2y4z3 is a term of degree 9.
degree API (°API)
a unit invented by the American Petroleum Institute (API) to measure the specific gravity, or one might say the "lightness," of petroleum. Lighter oils are more valuable, so the API scale gives them higher readings than heavier oils. If G is the specific gravity of the petroleum at temperature 60 °F (15.56 °C), the API degree rating is equal to (141.5/G) - 131.5 degrees.
degree Baumé (°B or °Bé)
a unit of relative density, as read on a type of hydrometer invented by the French chemist Antoine Baumé (1728-1804). Two scales are used, depending on whether the liquid is lighter than water or heavier than water. For lighter liquids, the relative density d in degrees Baumé is related to specific gravity G by the formula d = (144.3 / G) - 144.3.
degree Celsius (°C)
a metric unit of temperature. The Celsius temperature scale is named for the Swedish astronomer and physicist Anders Celsius (1701-1744), who used a similar scale. The freezing point of water (at one atmosphere of pressure) was originally defined to be 0 °C, while the boiling point is 100 °C. Thus the Celsius degree is 1/100 of the difference between these two temperatures. For practical purposes this is equivalent to the original definition. See also degree Fahrenheit, Kelvin. Please see Unit Table or Converter
degree centigrade (°C)
an older name for the degree Celsius. About 1850 scientists began calling the unit "degree Celsius".
degree day
a unit used in meteorology and engineering to measure the demand for heating or cooling. In the United States, it's agreed that 65 °F (18.3 °C) is the critical outside temperature; below this tempeature heating is needed and above it cooling is needed. The number of degree days recorded on a given date is equal to the difference between 65 and the mean temperature for that date (figured as the average of the highest and lowest temperatures). If the mean temperature is above 65, cooling degree days (CDD) are recorded; if it is below 65, heating degree days (HDD) are recorded.
degree Dornic (°D)
a measure of the acidity of milk. Each degree Dornic is equivalent to 0.01% lactic acid in the milk. Normal values are around 15.
degree EBC (°EBC)
a unit used in Europe to measure the color of beer. EBC is an abbreviation for European Brewing Convention. EBC degrees are related to the Lovibond degrees used in the U.S.  by the approximate formula °EBC = (°L * 2.65) - 1.2.
degree Fahrenheit (°F)
a unit of temperature used  in the United States. The unit was defined by the German physicist Daniel G. Fahrenheit (1686-1736), who also invented the mercury thermometer. Fahrenheit set 0° at the coldest temperature he could conveniently achieve using an ice and salt mixture, and it is said he intended to set 96° as the temperature of the human body.  On this scale, the freezing point of water (at normal sea level atmospheric pressure) turned out to be about 32 °F and the boiling point about 212 °F. The scale was precisely defined by these two temperatures:  °F =  9/5 °C + 32.
degree Kelvin (°K)
In the International System, temperatures on the absolute temperature scale are stated in kelvins, not in degrees Kelvin.
degree KMW (°KMW)
a unit used in Austria to measure the sugar content of must, the unfermented liquor from which wine is made.
degreeLovibond (°L)
a unit used in the U.S. to measure the color (really the darkness) of beer and honey. The scale is open-ended, but most readings fall between 1 (a very light gold, or yellow) and 25 (a very dark brown).
degree MacMichael (°McM)
a unit used to measure the viscosity, or thickness, of chocolate. Typical values range from around 60 °McM (very thin chocolates suitable for pouring into molds) to around 190 °McM (very thick chocolates).
degree Oechsle (°Oe)
a unit used in Germany and Switzerland to measure the sugar content of must, the unfermented liquour from which wine is made. One degree Oechsle (or Öchsle) is roughly equivalent to 0.2% sugar by weight. This unit is related legally to °KMW by the formula °Oe = °KMW * ([.022 * °KMW] + 4.54).
degree Plato (°P)
a unit measuring sugar content, especially of the wort, the unfermented liquour from which beer is made. Named for a German chemist, one degree Plato represents a sugar content equivalent to 1% sucrose by weight.  In Europe, beer is often taxed either by the degree Plato or by the actual alcohol content. There is no precise conversion between these quantities, but for tax purposes it is often assumed that 1% alcohol (1 degree) is equivalent to 2.5 degrees Plato; that is, 1 degree Plato is legally equivalent to 0.4% alcohol.
degree Quevenne (°Q)
a unit measuring the density of milk. 1 °Quevenne represents a difference in specific gravity of 0.001, so, for example, 20 °Q milk has specific density 1.020.
degree Rankine (°R)
a traditional unit of absolute temperature. 1 °Rankine represents the same temperature difference as 1 °Fahrenheit, but the zero point of the scale is set at absolute zero. This means the Rankine temperature is 459.67° plus the Fahrenheit temperature. 1 °Rankine is equal to exactly 5/9 kelvin. The unit is named for the British physicist and engineer William Rankine (1820-1872).
degree Réaumur (°r)
a unit of temperature formerly used in Europe. The Réaumur temperature scale is named for the French scientist René-Antoine Ferchault de Réaumur (1683-1757). It is similar to the Celsius scale in having its zero point at the freezing temperature of water, but the interval between the freezing and boiling temperatures of water equals 80 °r instead of 100 °C. Therefore, 1 °r equals 1.25 °C or 2.25 °F.
degree Soxhlet-Henkel (°SH)
a measure of the acidity of milk. Each degree Soxhlet-Henkel is equivalent to 0.0225% lactic acid in the milk. Normal values are around 7.
degree Therner (°Th)
a measure of the acidity of milk. Each degree Therner is equivalent to 0.009% lactic acid in the milk. Normal values are around 17.
degree Twaddle (°Tw)
a unit measuring the specific gravity of liquids denser than water. 1 °Twaddle represents a difference in specific gravity of 0.005 or 1/200, so a liquid of specific gravity S is measured at 200(S - 1) °Tw. For milk, 1 °Twaddle equals 5 °Quevenne (see above).
deka- (da-)
a metric prefix meaning 10, taken directly from the Greek word for ten, deka. The Latin spelling deca- is also used (see deca- above).
dekagram or decagram (dag)
a common metric unit of mass, the dekagram is frequently used in European food recipes. One dekagram is equal to 10 grams, 0.01 kilogram, or 0.352 739 66 ounce. The symbol dkg sometimes used for this unit is incorrect.
dekaliter or decaliter (daL or dal)
a metric unit of volume equal to 10 liters and comparable to the English peck. The dekaliter is equal to about 2.641 72 U.S. liquid gallons, 1.135 10 U.S. pecks, or 2.199 69 British imperial gallons (1.099 85 British pecks). The symbol dkL sometimes used for this unit is incorrect.
dekameter or decameter (dam)
a common metric unit of distance equal to 10 meters (about 32.8084 feet).
dekanewton or decanewton (daN)
a fairly common metric unit of force equal to 10 newtons. The dekanewton is equal to 1 megadyne, to 1.019 716 kilograms of force (kgf) or kiloponds (kp), to 2.248 09 pounds of force (lbf), and to 72.3301 poundals. In engineering, the dekanewton is a convenient substitute for the kilogram of force or kilopond, since it is nearly equal to those units.
a unit of angle measure equal to 10° or 1/36 circle. The ancient Egyptians divided the circle of the Zodiac into 36 divisions, which the Greeks called dekans.
dekare or decare
a metric unit of area equal to 10 ares, that is, 1000 square meters or 0.1 hectare. In English units, the dekare equals approximately 10 763.91 square feet, 1195.99 square yards, or 0.247 105 acres.
dekatherm or decatherm (DTH)
a unit of energy equal to 10 therms, 1 million Btu, or about 1.055 057 gigajoules (GJ).
a traditional prefix meaning 1/2. The prefix is derived from the Latin dimedius, meaning a cut in the middle of something.
a unit of relative time in music equal to 1/32 whole note or 1/64 breve.
dessertspoon or dessertspoonful (dsp or dssp)
a unit of volume sometimes used in food recipes. The dessertspoon is equal to 2 teaspoons; this is roughly equivalent to 10 milliliters in the U.S. In the metric world, a measuring spoon holding exactly 10 milliliters is often called a dessertspoon.
a unit of land area in Russia equal to 2400 square sadzhens. It equals about 1.0925 hectare or 2.6996 acres.
devil's dozen
an alternate name for the baker's dozen, a traditional unit of quantity equal to 13. This name reflects the long-standing association of the number 13 with bad luck or evil.
a logarithmic unit being used in astronomy. Originally, dex was a convenient function defined by dex (x) = 10x. But the notation is now being used after the exponent in expressions such as -.043 dex, meaning 10-.043. Thus 1 dex equals a factor of 10, making the dex identical to the bel. The name "dex" is a contraction of "decimal exponent."
a unit of land area in South Asia, equal to 1/20 kattha or 1/400 bigha. Like the bigha, the dhur varied in size from region to another. In Nepal, where the unit is still in use, the dhur equals about 16.9 square meters or 20.2 square yards.
a mysterious marking on many tape measures in the U.S. The diamonds mark a distance unit equal to exactly 8/5 feet (19.2 inches or 48.768 centimeters).
an old unit of distance equal to the width of a person's finger. Used in all the ancient civilizations of the Middle East and Mediterranean, the digit was equal to 0.75 inch or 19 millimeters with only the smallest variations. Typically, there were 4 digits in a palm, 16 in a foot, and 24 (sometimes 28) in a cubit. The word digit is from the Latin word for a finger or toe, digitus. It is used as any one in ten Arabic Numbers.
dimension (dim)
a mathematical unit measuring the number of independent directions in a set or space.  The ordinary space we live in has 3 dimensions. The theory of relativity is set in a "space-time" having 4 dimensions, and higher dimensional spaces are frequently used in science and economics. In addition, mathematicians have developed several methods for assigning fractional dimensions to certain complex sets.
a traditional Egyptian unit of distance equal to about 58 centimeters (22.8 inches).
dog year
an informal unit of time equal to 1/7 of a normal, or "human" year. According to folklore, dogs age 7 times faster than humans.
another name for a pair.
double word or doubleword
a unit of information equal to 2 shortwords, 4 bytes or 32 bits.
a familiar unit of quantity equal to 12. Division into units of 12 rather than 10 has the advantage that 12 can be evenly divided into halves, thirds, or quarters. For this reason, units of 12 have been common since the earliest civilizations of the Middle East. "Dozen" comes from an old French word dozaine related to the Latin word duodecem, "twelve."
an abbreviation for "dots per inch," remains in use even though individual picture elements are now called pixels rather than dots.
a traditional unit of weight in Greece and the eastern Mediterranean. The drachma was a Greek coin, and the unit was originally the weight of the coin. In ancient times this was about 4.3 grams, but more recent versions are about 3.2 grams, 49.3 grains, or 0.113 ounce avoirdupois. There is also a traditional Dutch weight unit of the same name, but it is somewhat larger: 3.906 grams, 60.28 grains, or 0.1374 ounce avoirdupois. Compared to a similar English unit, the Greek drachma is about 2.5 pennyweight and the Dutch is almost exactly 3 pennyweight.
a traditional unit of weight in France and Germany, generally between 3.7 and 3.9 grams.
a unit of weight in the traditional avoirdupois system, equal to 1/16 ounce or 1/256 pound. One dram equals about 1.7718 gram. The word dram comes from a Latin weight unit, the dragma, and derives ultimately from the Greek drachme, meaning a handful.

a unit of weight in the traditional system of English apothecaries, equal to 60 grains, 3 scruples, 1/8 troy ounce, or approximately 3.8879 gram. The apothecaries' dram is sometimes abbreviated dr. ap. to distinguish it from the avoirdupois dram.

a traditional unit of volume. See fluid dram.
a unit traditionally used in the textile industry to measure the density of a single fiber of yarn. One drex equals a density of one gram per 10 kilometers of length, or 1 microgram per centimeter (µg/cm). Since 1 drex equals 0.1 tex, the unit is now called the decitex (dtex)
drill sizes
traditional drill sizes are numbers 1-80, with larger numbers indicating smaller drills. Number 1 has diameter 0.2280 inch and number 80 has diameter 0.0135 inch. Larger sizes are designated by letters or by specifying the diameter directly in 64ths of an inch. The metric drill size is the diameter in millimeters.
a unit measuring the alcohol content of beverages, used in describing the medical effects of alcohol. U.S. physicians generally consider one drink equal to 0.5 U.S. fluid ounces of alcohol; the appropriate metric equivalent would be 15 milliliters. In U.S. fluid units, one drink corresponds to about 4 ounces of wine or 1.25 ounces of whiskey.
a traditional unit of weight in Scotland, equal to 1/16 Scots ounce or about 1.9 grams. Sometimes spelled drop, this unit was the Scottish counterpart of the English dram.
drop (gtt)
a unit of volume used in pharmacy. Now that prescriptions are written in metric units, the pharmacist's drop is equal to exactly 0.05 milliliter (20 drops/ml). In hospitals, intravenous tubing is used to deliver medication in drops of various sizes ranging from 10 drops/ml to 60 drops/ml. The traditional abbreviation is from the Latin gutta, drop. Originally, gt was the symbol for a single drop, with gtt being the plural.

a informal unit of volume used in recipes. According to some older kitchen references, 24 drops = 1/4 teaspoon; with U.S. definitions this makes the drop equal to 1/576 fluid ounce or about 0.051 milliliter, comparable to the pharmacist's drop.
drought severity category (D)
a measure of drought severity developed by the U.S. National Drought Mitigation Center and used widely by other agencies in the U.S. Categories are denoted D0-D5, with higher numbers indicating more severe drought.
a unit of volume sometimes used in the oil trade. The traditional standard drum of oil contains 55 U.S. gallons or about 208.198 liters. One 55-gallon drum equals 1.3095 barrels. In the metric world, drums of 200 liters, 205 liters, and 208 liters are in use as substitutes for the traditional size.
dry pint, dry quart
common names for the U.S. pint and quart units used for dry commodities, used to distinguish these units from the pint and quart used for liquids. The dry units are equal to about 1.163 647 times the corresponding liquid units.
duet or duo
a traditional unit of quantity equal to 2. The word duet is a French version of the Italian duo, two.
dunum or donum
a traditional unit of land area in the Middle East and the Balkans. The unit is of Turkish origin, but it seems to be obsolete in modern Turkey. As it is commonly used today in Israel and Palestine and in Croatia and other areas of the former Yugoslavia, the dunum is a metric unit equal to 1000 square meters or 0.1 hectare (about 0.2471 acre).  In Mesopotamia and Arabia, the dunum was a larger unit, traditionally in the range of 2500 to 4000 square meters. In modern Iraq, the dunum is now standardized at 2500 square meters (about 0.6179 acre).
duro, durometer
a measure of the hardness of plastic, rubber, or similar material, made an instrument called a durometer. These instruments test the material with a steel pin, and the depth of the indentation made by the pin is read by a calibrated spring meter.


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