- If we did, we would have to change the definition of the metre each time we were able to make a more precise laser.
- Yes, magnetic fields - and indeed magnetically permeable materials close to a balance - can effect a weighing result.
- The short answer is 'both', because the use of the word midnight is heavily dependent on its context.
- Accurate measurement of thermal conductivity is not quite as straightforward as the simple steady-state theory would suggest.
- No, the difference is not very meaningful at all.
- The triple point temperature of a pure substance is the unique temperature at which the solid, liquid and vapour phases of the substance co-exist in thermal equilibrium. Such triple points make ideal reference points for the calibration of thermometers.
- The measurement uncertainties associated with specifications for force-measuring devices are often expressed as a percentage of full-scale reading. This is not always the case, however, and sometimes percentage of reading is used instead and the differences can be very significant, particularly when measuring forces that are quite small for a particular instrument.
- There is no fixed period for the validity of a calibration certificate - it is not like your cars MOT certificate. However, measurement results stated on certificates are usually 'on the day' values and no allowance is made for subsequent drift.
- 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.