- The gigasecond is the only scientifically-preferred time interval that is passed in adult life.
- Yes it does - provide that you mean the 'scientific' definition of weight where the weight of a body is the gravitational force acting on it and hence it should be measured in newtons; this force depends on the local acceleration due to gravity.
- NPL gets the traceability of its 300 mm diameter Master Flat from the surface of a pool of silicone oil, which conforms to the local radius of curvature of the earth and from which the departure from flatness can easily be calculated.
- 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.
- We would recommend that reference flats in interferometers be recalibrated every three to five years depending upon the precision of measurement required.
- 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.
- No, they are not. The internationally recognised SI unit for pressure is the pascal, abbreviated to Pa, and this is the unit realised by the primary measurement standards in the world's national metrology institutes to provide traceability for pressure measurements.
- The International Prototype Kilogram is not perfectly stable (its mass changes with time), the amount it changes cannot be known perfectly (there is no 'perfect' reference against which to judge it) and the values of the national copies cannot be monitored at the highest level of accuracy without being compared directly with it.
- The most accurate barometers are indeed the mercury primary barometers used at national measurement institutes. Most barometers, though, are secondary instruments rather than primary ones and when considering these it is not correct to say that those based on a mercury column are invariably more accurate than those that are based on an alternative principle.
- Yes there are - some are listed here.
- Up to a point yes, but unless a weight is of suitable design and material and in appropriate condition it will not be possible to give it a meaningful calibration and it would certainly be a waste of money.
- Give the weight a general inspection to check its construction, surface finish and the suitability of its magnetic properties.
- A number of factors need to be taken into account when considering sources for calibrating radiation thermometers.
- Yes - Saturated (or unsaturated) salt solutions, and certain other chemicals, can be used to generate an environment of a particular relative humidity in an enclosed space.
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