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3. Прочитайте текст снова и письменно ответьте на вопросы:

1. What role does the National Institute of Standards and Technology play in the USA?

2. Who makes periodic inspections to verify compliance, maintaining the integrity of commercial measurements?

3. What does commercial measurement generally involve?

4. Does the NIST enforce measurement accuracy directly?

5. What do Highway State Police and the State Highway Department generally run?

ВАРИАНТ 4

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MEASUREMENT AND STANDARDS

1. Measurement is the process of associating numbers with physical quantities and phenomena. The process is accomplished through the comparison of a measured value with some known quantity (standard) of the same kind. The subject has become of vital importance in sciences, engineering and to much everyday activity.

2. While measurement theory began with the Greeks in the 4th century BC, the first useful work appeared in the 18th century by English mathematician Thomas Simpson on observation error – perhaps the most important single aspect of measurement theory.

3. The acceptance of measurement standards is vital if the measurements are to be meaningful to others. The first known widely used standard was the Egyptian cubit. It was the standard of length (0.4511meters) that came into use around 3000 BC and was maintained as a length of black granite This was effectively the primary standard against which other cubit sticks (secondary standards) were regularly compared. The definition of the cubit changed from time to time as a result of political and national issues.

4. In principal the cubit standard was similar to the meter standard up until 1960. The meter was adopted by France in 1795, and for a long time was a length of indium rod. From 1960 the meter was redefined in terms of the wavelength of krypton light (the meter was set to be 1,650,763.73 wavelengths in vacuum of the orange-red line of the spectrum of krypton-86).

5. Similarly other standards have evolved, with the System International (SI) now having by far the widest acceptance, especially amongst the scientific community. Interestingly the unit of mass – the kilogram – is the only basic standard that is now represented by a physical object. An international effort is underway to establish a new and absolute definition of the kilogram in terms of a number of silicon atoms. Physically, a very precisely manufactured sphere of pure single crystal silicon (as in microelectronics) will become the practical standard, but it will be defined in terms of the number silicon atoms it contains.

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3. Прочитайте текст снова и письменно ответьте на вопросы:

1. What is measurement?

2. When did measurement theory begin?

3. What was the first known widely used standard?

4. What standard was the cubit standard similar to up until 1960?

5. What is the unit of mass?

ВАРИАНТ5

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MODERN STANDARDS

1. Standards are objects or ideas that are designated as being authoritative for some accepted reason. Whatever value they possess is useful for comparison to unknowns for the purpose of establishing or confirming an assigned value based on the standard. The design of this comparison process for measurements is metrology. Metrology is the science of measurement. The execution of measurement comparisons for the purpose of establishing the relationship between a standard and some other measuring device is calibration.

2. Currently, only five independent units of measure are internationally recognized: temperature interval, linear distance, electrical current, frequency and mass. All measurements of all types are based on one or more of these independent units. Two supplemental independent units are also recognized internationally, both dealing with angle measurement. For example, Ohm's law is a widely known concept in electrical study. Of the three units of measure involved, only current (ampere) is an independent unit. Voltage and resistance units are dependent on current units, as defined by Ohm's law.

3. It is believed that each of independent units of measure will be defined in terms of the other four independent units eventually. Length (meter) and time (second) are already connected this way. If an accurate time base is available, then a length standard can be reproduced without a meter bar artifact, using the known constant speed of light. Lesser known is the relationship between the luminance (candela) and current (ampere). The candela is defined in terms of the watt, which in turn is derived from the ampere. This difficult to recreate standard is supplemented by an incandescent bulb design that is used as a secondary and transfer standard. These bulbs recreate the candela when a specific amount of current is applied.

4. The development of standards follows the needs of technology. As a result, some units of measure have much more resolution than others.