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- There are a number of possible reasons for the difference, in addition to possible calibration errors.
- As infrequently as possible.
- The short answer is 'both', because the use of the word midnight is heavily dependent on its context.
- The name "kilogram" is a historical quirk.
- There are commercial organisations that are accredited for this purpose.
- For a given composition and temperature, air density varies in direct proportional to air pressure and this reduces with altitude for two reasons - both related to gravity.
- The MSF time signal provides a good service throughout the British Isles, with signal strengths greater than 100 µV/m at 1000 km from Anthorn (in Cumbria) in all directions.
- An air buoyancy correction has to be made, where the measurement uncertainty required of a weighing warrants it, when the volumes (and hence the amount of displaced air) of two masses being compared are different.
- 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.
All FAQs
- The name "kilogram" is a historical quirk.
- Platinum-iridium was chosen as the material for the kilogram for a number of reasons.
- Many old pressure units have obvious practical and historical origins; for example, inches of water was the unit used where pressures were measured with a water column whose top surface was sighted against an inch scale.
- Discussions in Europe under the MERA project are pointing in the direction of this alternative to a single world or European institute, but some duplication and collaboration will probably always be required.