- The words accuracy and uncertainty are sometimes interchanged but the difference between them is significant and, in many applications it is vital.
- A pressure balance is simply an alternative name for a piston gauge (more frequently spelt piston 'gage').
- Mass is therefore a base quantity in the SI and its unit is the kilogram, which is abbreviated to kg.
- To some degree yes. Ideally, the reflectivity of both the reference and test surface should be equal to give maximum contrast fringes.
- Calibration is defined as a set of operations that establish, under specified conditions, the relationship between the values of quantities indicated by a measuring instrument or measuring system … and the corresponding values realised by standards.
- The (international) inch has been exactly 25.4 mm since July 1959. At this point in time the (international) yard was redefined as 0.9144 metre.
- There is no clear boundary between pressure and vacuum and the word vacuum simply refers to part of the pressure scale. Its definition is not precise but it is commonly taken to mean pressures below, and often considerably below, atmospheric pressure.
- Since 1995 October 22 there has been a permanent one-hour difference between British time (as broadcast by MSF) and Central European Time, as broadcast by DCF-77 in Germany.
- 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.
- 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.
Please note that the information will not be divulged to third parties, or used without your permission