- Values of atmospheric pressure in Teddington, measured at about 10 metres above sea level, going back to 1 January 1998 and shown both graphically and digitally, can be found on the historical pressure page of the NPL on-line barograph.
- No. Since 1983 the metre has been re-defined in terms of the speed of light and is realised using laser wavelengths.
- Metrology is a service discipline - responding to a perceived need for a particular measurement accuracy, either now or in the near future.
- The Système International d'unités - the SI system - is the coherent system of units adopted and recommended by the General Conference on Weights and Measures (CGPM). It is based on seven base quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity.
- The words accuracy and uncertainty are sometimes interchanged but the difference between them is significant and, in many applications it is vital.
- There are difficulties in displaying the time of day on internet pages...
- A blackbody source is an ideal, 'Planckian', radiator, i.e it emits thermal (visible and infrared) energy whose intensity at a given wavelength and temperature is given by the Planck Law of radiation.
- In Europe the weight classification system adopted is that produced by the International Organization of Legal Metrology (OIML), known as document OIML Recommendation R 111.
- 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.
Please note that the information will not be divulged to third parties, or used without your permission