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- The length of time that it will take for the step gauge to reach ambient temperature in the laboratory will depend on both its mass and the temperature differential between the car boot and the laboratory.
- As UTC is running about one second per year faster than time based on the Earth's rotation (Greenwich Mean Time, or Universal Time), an extra second is occasionally inserted in the UTC time scale to let it fall behind and start catching up again.
- Force is a measure of the interaction between bodies, mass is a measure of the amount of material in an object, weight is the gravitational force acting on a body (although for trading purposes it is taken to mean the same as mass) and load usually means the force exerted on a surface or body.
- No. Since 1983 the metre has been re-defined in terms of the speed of light and is realised using laser wavelengths.
- Calibration is defined as a set of operations that establish, under specified conditions, the relationship between the values of quantities indicated by a measuring instrument or measuring system … and the corresponding values realised by standards.
- For the last 20 years there has been a considerable amount of work undertaken looking for an alternative, more fundamental, definition for the SI unit of mass - the kilogram.
- SI units are divided into two classes, base units and derived units. The base units are dimensionally independent.
- There are difficulties in displaying the time of day on internet pages...
- The services of NPL are equivalent to those offered by NIST (and other National Labs), as covered by the Mutual Recognition Arrangement.
- When converting between pressure units consideration should be given to the number of significant figures to use, bearing in mind that many of the underlying conversion factors are not themselves exact and cannot be made so.
All FAQs
- Calibration is defined as a set of operations that establish, under specified conditions, the relationship between the values of quantities indicated by a measuring instrument or measuring system … and the corresponding values realised by standards.
- Sometimes, the word calibration is misused to describe the process of altering the performance of an instrument to ensure that the values it indicates are correct within specified limits, strictly this is adjustment.
- Density is defined as mass per unit volume; it has the SI unit kg·m-3 and is an absolute quantity. Specific gravity is the ratio of a material's density with that of water at 4 °C and is therefore a relative quantity with no units.
- A transducer is a device that provides an output quantity having a determined relationship to the parameter being measured - force in this case.
- In 1790 the French National Assembly obtained Louis XVI's assent to commission the country's leading scientists to recommend a consistent system for weights and measures.
- The ITS-90 (International Temperature Scale of 1990) defines procedures by which certain practical thermometers of the required quality and precision can be calibrated in such a way that the values obtained from them can be precise and reproducible, while at the same time representing the corresponding thermodynamic temperatures as closely as possible.
- Pressure balances operate over a pressure range extending from about 3 kPa to 1 GPa. Any one piston-cylinder can only be used over a pressure range that typically varies from about 10:1 up to about 100:1.
- A difficult question perhaps impossible. In what way the minimum? Some would say seven have been introduced into the SI because seven are needed. It has also been argued that with the use of fundamental constants only one unit is needed.
- No dimensioned measurement can be made more accurately than its corresponding SI unit is known. Thus the measurements with the smallest uncertainty are those of frequencies as the second is the most precisely realised unit.
- When they started in 1950 the MSF signals carried only seconds and minute markers, without any labels. In September 1974 a short burst of data at 100 bit/s was added during the first second of the minute to signal the hour and minute - the 'fast code'.