Measurements of physical characteristics are used widely in everyday human life, whether in household or industrial processes, in service or in scientific researches. Some of the main categories of regularly measured parameters are weight, length, area, volume, temperature, density, concentration, voltage, amperage and power. Measurement units historically differed from nation to nation, but over time there is a straight tendency for unification of units.

Metric system is recognized as universal in ever-growing number of countries and this allows to minimize differences and errors in international scientific, trade and other types of communications.

In metric system, meter, its multiples and fractionals are used for the measurements of length, square meter and its derivates are for measurements of area, cubic meter – for measurements of volume. For measuring temperature there are Celsius or Fahrenheit degrees used, for measuring density – kilogram per cubic meter. Voltage in international metric system is measured in volts, amperage – in amperes, and watts are used for measuring power.

To perform measurements one needs to have appropriate instruments.

These instruments should have accuracy grade acceptable for the type and purpose of measurements that will be performed. When measurement of length is performed, the only kind of instruments needed is tape-measure or straight scale, if size of measured object is relatively small. If distance that has to be measured is large, and surface between starting and finishing points is not smooth, more sophisticated instruments will be needed to perform required measurements.

Measurements of area and volume will sometimes require certain calculations in addition to direct measurements. If measurement of an area of regular shape is performed, it is enough to measure length of the sides of that area and then apply relatively simple formulas for calculation of that area. But if the area measured has irregular shape with edges of bizarre form, calculations will be far more complex and may require solution of integral equations to determine approximate size of an area in question. When it is necessary to measure volume of a liquid, volumetric glassware is enough.

But when the volume of a body with complex form shall be calculated, procedure of measurement may become much more complicated. If the body with unknown volume is available for direct measurement, it may be submerged into the water or any other liquid and volume of displaced liquid that is equal to the volume of that body, could be measured. But if that body is not available for direct measurement and is given in form of a scheme with known parameters measured or set beforehand, then rather complicated calculations may be required to estimate the volume of a said body.

Density of a liquid may be measured using special instrument called densitometer, which is based on displacement of a certain amount of liquid by the weight of the instrument. The higher density of examined liquid, the smaller will be volume of liquid displaced. For estimation of the density of gases or solid bodies another methods shall be applied, because displacement-based densitometry cannot be applied to non-liquid substances. Measurements of mass and volume are usually performed, and density then is calculated using the simple formula of mass divided by volume.

Temperature can be measured using thermometers of different types – liquid-filled, electric, etc. Electric parameters like amperage, voltage and power, could be measured either directly using specific measuring devices, or indirectly by measuring related parameters and later calculating values of parameters required. For a list of physical parameters there are specific units in the system of measurements. Some of the examples were given above. For another example, unit for measuring force is newton, and unit for pressure is pascal.

Certain parameters can be formulated indirectly through other units. Speed, for example, is defined as unit of distance passed per unit of time, and acceleration – as rate of change of speed per unit of time. Consequently, force that influences a body, may be calculated through known mass of the body, its beginning speed and rate of change of its speed under the influence of the force studied. Unfortunately, measurements can never provide us with absolute values of parameter we are interested in.

Due to imperfection of both human perception, instruments for measurements and because of influence of unstable environmental conditions upon the instrument, body that is subjected to measurements and the person performing measurements, some imprecision will always be present. Additionally, when performing measurements, observer sometimes has to use estimated data because more or less precious values can not be obtained under current conditions. Or maybe high precision values of a given parameter are not important for the current task. Either way, estimation of measured data sometimes takes place, as well as certain ever-present