Metrology is the science that focuses on the study of the principles, methods, and means necessary to perform the measurement of physical quantities. It also studies the methods of execution and the determination of errors. It is fundamental that the properties of an object or phenomenon must be measurable, meaning it must be possible to define units of measurement and measurement methods.+2
1.1 What is a measurement?
The measurement of a physical quantity is the number that expresses the ratio between the quantity under examination and the reference quantity.
- Example: If a mechanical component has a thickness of 5 millimeters (mm), it means its thickness is 5 times the unit of measurement, which in this case is the millimeter.
1.2 What is a unit of measurement?
To measure a physical quantity, it is compared with one of the same kind, that is, with a unit of measurement, which is the quantity chosen as a standard. The unit of measurement (and therefore its standard) must be compatible, meaning adequate for the dimensions of the object or phenomenon we wish to explore and measure. After defining a unit of measurement, in practice, an appropriate multiple or submultiple is adopted.+2
Figure 1. Multiples and submultiples in the SI
| SI MULTIPLES | SI SUBMULTIPLES | ||
| Prefix / Symbol | Value | Prefix / Symbol | Value |
| exa- (E) | $10^{18}$ | deci- (d) | $10^{-1}$ |
| peta- (P) | $10^{15}$ | centi- (c) | $10^{-2}$ |
| tera- (T) | $10^{12}$ | milli- (m) | $10^{-3}$ |
| giga- (G) | $10^9$ | micro- ($\mu$) | $10^{-6}$ |
| mega- (M) | $10^6$ | nano- (n) | $10^{-9}$ |
| kilo- (k) | $10^3$ | pico- (p) | $10^{-12}$ |
| hecto- (h) | $10^2$ | femto- (f) | $10^{-15}$ |
| deca- (da) | $10^1$ | atto- (a) | $10^{-18}$ |
To obtain a measurement, two methods can be used:
- 1.3 Direct measurement
- 1.4 Indirect measurement
1.3 Direct measurement
This occurs when the unit of measurement is compared directly with the quantity to be measured and the number of units contained in the measured quantity is established.
- Examples: Measurable directly are the width of a glass pane, the weight of a metal bolt, the depth of a hole, or the diameter of a piston.
1.4 Indirect measurement
An indirect measurement occurs when other measurements performed directly are processed using mathematical products and/or ratios.
- Examples: Measured indirectly are the surface area of a residential floor, the density of a liquid alloy, or the average speed of a conveyor belt.
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