- Density is defined as mass per unit volume; it has the SI unit kg·m-3 and is an absolute quantity. Specific gravity is the ratio of a material's density with that of water at 4 °C and is therefore a relative quantity with no units.
- Many factors will have an influence on how well a mass balance or comparator will perform. One key factor is the location and environment in which the balance is located.
- 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.
- This is an arrangement amongst the majority of the world's National Metrology Institutes whereby each institute agrees to recognise measurement standards and calibration and measurement certificates issued by the other.
- The figures in the table below represent typical characteristics but force transducers and force measurement systems will often operate outside these ranges with increased measurement uncertainty.
- The measurement uncertainties achievable with pressure gauges, particularly traditional circular 'dial' gauges, are often expressed in one of two ways - as a percentage of reading or as a percentage of full-scale reading and the differences can be very significant, particularly when working at pressures much lower than an instrument's full-scale.
- Probably not. The figures should be interpreted with caution, especially if an instrument has not been independently calibrated for some time.
- Yes there is a difference.
- 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.
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