- There are no 'official' definitions of the duration of spring, summer, autumn and winter for civil purposes. Many bodies, for example meteorologists, adopt a convention for the purpose of presenting statistics by grouping the twelve months of the year into four three-month seasons.
- The variation in the value of g across the earth's surface is about 0.5 % due to latitude, plus a change of approximately 0.003 % per 100 m altitude. Local topography and tidal forces also can have small effects.
- To the best of our knowledge, the NPL on-line barograph is unique inasmuch as it provides a fully traceable pressure measurement, with a properly calculated uncertainty, and also allows historical data to be displayed both graphically and digitally.
- 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.
- 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.
- The micrometre (0.001 mm) gauge should be taken first, followed by the hundredth, tenth and millimetre gauges.
- 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.
- The time at which summer time begins and ends is given in the relevant EU Directive and UK Statutory Instrument as 1 a.m. Greenwich Mean Time (GMT).
- 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.