- The letters are meant to stand for gauge-mode and absolute-mode respectively - where a gauge-mode pressure is one normally measured with respect to ambient pressure and an absolute-mode pressure is one measured with respect to zero pressure.
- Yes it can in some circumstances but, where it does, it is fairly easy to ensure that its effect on the measurement uncertainties obtained is negligible.
- What is evolving is our knowledge of the constants not as far as we know their values, which for the purposes of evaluation are considered constant.
- GPS has its own date and time scale for expressing satellite positions, based on counting weeks, and seconds within a week. To limit the size of the numbers used in the data and calculations the GPS Week Number is a ten-bit count in the range 0-1023, repeating every 1024 weeks.
- The terms high- and low- (and also medium-) vacuum are not very intuitive; they are used to describe the various pressure ranges known under the general banner of vacuum but are neither defined nor used consistently.
- In 1799 it was agreed that the unit should be the mass of one cubic decimetre of water at a temperature of 4 °C, which would be called a kilogram (kg). The mass of one cubic centimetre of water would be called a gram (g).
- NPL offers a cost-effective re-certification service after the initial certification period has expired.
- No dimensioned measurement can be made more accurately than its corresponding SI unit is known. Thus the measurements with the smallest uncertainty are those of frequencies as the second is the most precisely realised unit.
- 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.