measurements

Measurement is the act of quantifying a property of a phenomenon or object by comparing it to a reference standard using a defined unit. Measurements assign numbers to attributes such as length, mass, time, and temperature, and can extend to derived properties like speed or density. The process typically involves selecting a unit, using a measurement instrument, and recording the result.

The International System of Units (SI) provides a coherent framework of base and derived units. Base units include the meter, kilogram, second, ampere, kelvin, mole, and candela; derived units combine these. Many fields also use non-SI systems, but SI with traceability to standards is the foundation of modern science.

Measurements are linked to standards through traceability, ensuring comparability across times and places. Primary standards are maintained by national or international bodies such as the BIPM and NIST, with instruments calibrated to ensure accuracy.

No measurement is perfectly exact. Every result has uncertainty arising from instrument limits, environment, and observer effects. Accuracy concerns closeness to the true value, while precision concerns repeatability. Results are reported with an uncertainty and, often, with significant figures.

Measurement methods vary: direct measurements use a single instrument, while indirect measurements rely on calculations from multiple readings. Common tools include rulers, balances, thermometers, calipers, and spectrometers, each requiring calibration.

In science and industry, measurement underpins experimentation, quality control, and standardization, enabling comparisons, replication, and reliable commerce. The practice rests on clear definitions, standardized units, proper calibration, and careful documentation.