Every day there situations arise when a certain measurement is required – be it in household or in hospital, in industry or in the field. But, whenever it may be, there are certain considerations that should be done towards measurements. Main consideration is approximate character of every measurement. This means that one can never obtain absolute value of the parameter he measures. Even if measurements will be performed using ideal measuring instruments, due to imperfect perception of the person performing measurements some difference in data obtained through the measurements will be present.
Even more, several measurements performed in succession, will most likely produce slightly different results even if an ideal instrument will be used for performing those measurements. This difference may be more or less significant depending of precision of the measuring instruments used, but it will still be present. Difference between approximate value gained through measurement and absolute value of measured parameter may arise from various sources. In practice, there are several sources simultaneously contributing to rise of measurement errors.
It is possible to make errors contributed by every source less significant, but not to nullify these errors. In the following certain main sources of errors during measurement will be explained. Influence of external physical factors upon measuring instrument may cause changes of physical properties and parameters of that instrument. For example, thermal dilation of graduated bottles may change actual volumes and generate difference between actual and measured value.
Second source of errors is imperfect perception of the person performing measurements. Resolution ability of human eye are limited, and some degree of error still may be present even if magnifying devices are used. Third source is imperfection of instruments that are used for measurements, and devices that are used for manufacturing those instruments. It is impossible to create an absolute copy of reference instrument, certain difference between copy and original would always be present.
There are two main ways to fight these uncertainties in measurements. First is minimization of impacts of all sources of errors. Second is to estimate approximate scale of errors for every given instrument and use this knowledge afterwards. This approximate scale of possible errors is called precision of an instrument. Precision is is put in certain parts of measurement unit used, or in percents of measuring span. With the same precision number, the larger unit of measurement will be used, the larger size of deviation within precision scale will be.
For instance, with precision of 0,01%, when meter is used, acceptable errors in measurements will be in range of 0,1 mm. But when kilometer is used as measurement unit, with the same precision acceptable errors will be in range of 10 cm, which is more significant difference for a human. In certain cases high precision is not critical to the final result. For example, when measurements of parallactic angles are performed, precision is not highly critical because star is still visible and located inside the certain radius on the celestial sphere.
Another example is detection of location of marathon runners using GPS-devices. As far as it s still possible to receive precise data from local observers, scale of differences within 450-500 meters is perfectly acceptable. But in certain other situations high precision is mandatory. Good example of such case may be production of highly potent drugs where amounts of active substances are measured in millesimal parts of gram. Failures may result in accidental overdosing of the drug and severe consequences to the patient.
The same is truthful for laboratory analyses, when precise amounts of reagents are critical and may affect the outcome of an analysis greatly, which can lead to diagnostic errors, and to certain chemical production processes where slight differences in amounts of some reagents may result in instability of the reaction mixture and probably detonation or damage to the apparatus, left alone incorrect reaction behaviour and undesired outcome in the form of unwanted products of the reaction.