Measurement is the assignment of a number to a characteristic of an object or event, which can Six of these units are defined without reference to a particular physical object which serves as a standard (artifact-free), while the . One device for measuring weight or mass is called a weighing scale or, often, simply a scale. A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention In the social sciences, there are no standard units of measurement and the theory and practice of the need to relate the two units might arise, and consequently the need to choose one unit as defining the other or viceversa. 1. Methods Mol Biol. ; doi: /_5. Nitric Oxide (NO) Measurements in Stomatal Guard Cells. If time-course measurements are needed, the epidermis can be adhered to a cover-glass or glass slide.
Required 1 – No Measurements
Both the imperial units and US customary units derive from earlier English units. Imperial units were mostly used in the British Commonwealth and the former British Empire. US customary units are still the main system of measurement used in the United States outside of science, medicine, many sectors of industry, and some of government and military, and despite Congress having legally authorised metric measure on 28 July While the above systems of units are based on arbitrary unit values, formalised as standards, some unit values occur naturally in science.
Systems of units based on these are called natural units. Similar to natural units, atomic units au are a convenient system of units of measurement used in atomic physics. Also a great number of unusual and non-standard units may be encountered. To reduce the incidence of retail fraud, many national statutes have standard definitions of weights and measures that may be used hence "statute measure" , and these are verified by legal officers.
In informal settings, a quantity may be described as multiples of that of a familiar entity, which can be easier to contextualise than a value in a formal unit system. For instance, a publication may describe an area in a foreign country as a number of multiples of the area of a region local to the readership. The propensity for certain concepts to be used frequently can give rise to loosely defined "systems" of units.
Different systems of units are based on different choices of a set of base units. There are seven SI base units.
All other SI units can be derived from these base units. For most quantities a unit is necessary to communicate values of that physical quantity. For example, conveying to someone a particular length without using some sort of unit is impossible, because a length cannot be described without a reference used to make sense of the value given. But not all quantities require a unit of their own.
Using physical laws, units of quantities can be expressed as combinations of units of other quantities. Thus only a small set of units is required. These units are taken as the base units. Other units are derived units. Derived units are a matter of convenience, as they can be expressed in terms of basic units. Which units are considered base units is a matter of choice. Any value of a physical quantity is expressed as a comparison to a unit of that quantity.
For example, the value of a physical quantity Z is expressed as the product of a unit [Z] and a numerical factor:. The multiplication sign is usually left out, just as it is left out between variables in scientific notation of formulas. The conventions used to express quantities is referred to as quantity calculus. In formulas the unit [Z] can be treated as if it were a specific magnitude of a kind of physical dimension: Units can only be added or subtracted if they are the same type; however units can always be multiplied or divided, as George Gamow used to explain.
A distinction should be made between units and standards. A unit is fixed by its definition, and is independent of physical conditions such as temperature. By contrast, a standard is a physical realization of a unit, and realizes that unit only under certain physical conditions. For example, the metre is a unit, while a metal bar is a standard. One metre is the same length regardless of temperature, but a metal bar will be exactly one metre long only at a certain temperature.
Conversion of units involves comparison of different standard physical values, either of a single physical quantity or of a physical quantity and a combination of other physical quantities. Or, which is just mathematically the same thing, multiply Z by unity, the product is still Z:. Or as an example using the metric system, you have a value of fuel economy in the unit litres per kilometres and you want it in terms of the unit microlitres per metre:.
It is the world's most widely used system of units , both in everyday commerce and in science. The SI was developed in from the metre-kilogram- second MKS system, rather than the centimetre-gram-second CGS system, which, in turn, had many variants. During its development the SI also introduced several newly named units that were previously not a part of the metric system.
The original SI units for the seven basic physical quantities were: The mole was subsequently added to this list and the degree Kelvin renamed the kelvin. There are two types of SI units, base units and derived units. Base units are the simple measurements for time, length, mass, temperature, amount of substance, electric current and light intensity.
Derived units are constructed from the base units, for example, the watt , i. The SI allows easy multiplication when switching among units having the same base but different prefixes.
To convert from metres to centimetres it is only necessary to multiply the number of metres by , since there are centimetres in a metre. Inversely, to switch from centimetres to metres one multiplies the number of centimetres by 0. A ruler or rule is a tool used in, for example, geometry , technical drawing , engineering, and carpentry, to measure lengths or distances or to draw straight lines.
Strictly speaking, the ruler is the instrument used to rule straight lines and the calibrated instrument used for determining length is called a measure , however common usage calls both instruments rulers and the special name straightedge is used for an unmarked rule. The use of the word measure , in the sense of a measuring instrument, only survives in the phrase tape measure , an instrument that can be used to measure but cannot be used to draw straight lines.
As can be seen in the photographs on this page, a two-metre carpenter's rule can be folded down to a length of only 20 centimetres, to easily fit in a pocket, and a five-metre-long tape measure easily retracts to fit within a small housing. The Australian building trades adopted the metric system in and the units used for measurement of length are metres m and millimetres mm.
Centimetres cm are avoided as they cause confusion when reading plans. American surveyors use a decimal-based system of measurement devised by Edmund Gunter in A link is abbreviated "lk," and links "lks" in old deeds and land surveys done for the government. Time is an abstract measurement of elemental changes over a non spatial continuum.
It is an apparently irreversible series of occurrences within this non spatial continuum. It is also used to denote an interval between two relative points on this continuum. Mass refers to the intrinsic property of all material objects to resist changes in their momentum. Weight , on the other hand, refers to the downward force produced when a mass is in a gravitational field.
In free fall , no net gravitational forces objects lack weight but retain their mass. The Imperial units of mass include the ounce , pound , and ton. The metric units gram and kilogram are units of mass. One device for measuring weight or mass is called a weighing scale or, often, simply a scale.
A spring scale measures force but not mass, a balance compares weight, both require a gravitational field to operate. Some of the most accurate instruments for measuring weight or mass are based on load cells with a digital read-out, but require a gravitational field to function and would not work in free fall. The measures used in economics are physical measures, nominal price value measures and real price measures. These measures differ from one another by the variables they measure and by the variables excluded from measurements.
In the field of survey research, measures are taken from individual attitudes, values, and behavior using questionnaires as a measurement instrument. As all other measurements, measurement in survey research is also vulnerable to measurement error , i. In order to get accurate results, when measurement errors appear, the results need to be corrected for measurement errors.
Since accurate measurement is essential in many fields, and since all measurements are necessarily approximations, a great deal of effort must be taken to make measurements as accurate as possible. Using physics, it can be shown that, in the gravitational field of the Earth, it should take any object about 0.
However, the following are just some of the sources of error that arise:. Additionally, other sources of experimental error include:. Scientific experiments must be carried out with great care to eliminate as much error as possible, and to keep error estimates realistic. In the classical definition, which is standard throughout the physical sciences, measurement is the determination or estimation of ratios of quantities.
The classical concept of quantity can be traced back to John Wallis and Isaac Newton , and was foreshadowed in Euclid's Elements. In the representational theory, measurement is defined as "the correlation of numbers with entities that are not numbers". The first attempt to incorporate measurement theory into the social sciences also occurred in the 18th century, when Jeremy Bentham , a British utilitarian moralist, attempted to create a theory for the measurement of value.
Since most social theories are speculative in nature, attempts to establish standard measuring sequences or techniques for them have met with limited success. Some of the problems involved in social measurement include the lack of universally accepted theoretical frameworks and thus of quantifiable measures, sampling errors, problems associated with the intrusion of the measurer on the object being measured, and the subjective nature of the information received from human subjects.
Economics is probably the social science that has had the most success in adopting measurement theories, primarily because many economic variables like price and quantity can be measured easily and objectively.
Demography has successfully employed measurement techniques as well, particularly in the area of mortality tables. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind.
Your contribution may be further edited by our staff, and its publication is subject to our final approval. Unfortunately, our editorial approach may not be able to accommodate all contributions. Our editors will review what you've submitted, and if it meets our criteria, we'll add it to the article. Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed.
The Editors of Encyclopaedia Britannica. Read More on This Topic. Learn More in these related Britannica articles: Instrumentation , in technology, the development and use of precise measuring equipment. Although the sensory organs of the human body can be extremely sensitive and responsive, modern science and technology rely on the development of much more precise measuring and analytical tools for studying, monitoring, or controlling all kinds of phenomena.
Telemetry , highly automated communications process by which measurements are made and other data collected at remote or inaccessible points and transmitted to receiving equipment for monitoring, display, and recording. Originally, the information was sent over wires, but modern telemetry more commonly uses radio transmission. Basically, the process is the same…. The development of quantitative science. Yet this activity would be no more than the compiling of a catalog of facts unless an underlying recognition of uniformities and correlations enabled the investigator to choose what to measure out….
They are based on the metric system, first adopted officially by France in Other units, such as those of the British engineering system, are still in use in…. More About Measurement 20 references found in Britannica articles Assorted References major reference In measurement system instruments In hand tool: Plumb line, level, and square metrology In metrology molecular weights In liquid: Colligative properties quantum mechanics paradoxes In philosophy of physics: The measurement problem In quantum mechanics: Axiomatic approach In quantum mechanics: A quantum voltage standard speed of light significance In electromagnetic radiation: Speed of light units In mechanics: Units and dimensions applications accounting In accounting: Measurement standards View More.
Articles from Britannica Encyclopedias for elementary and high school students.
Page 1 to global markets that are fair and open and without unnecessary barriers to trade. In some industries the need for accurate measurement is critical. What are the minimum number of measurements required to generate a Although no longer published, he (Butler) has placed it online at . The gaussian or normal distribution is only one of the many distributions a data set may obey. Experimental uncertainties should be rounded to one significant figure. Estimating the uncertainty in a single measurement requires judgement on the part cases are the same thickness and that there is no space between any of the cases.