Glossary — Foundations of physics
Absolute uncertainty — the uncertainty of a measurement written in the same unit as the measurement, such as in .
Accuracy — how close a reading is to the true value.
Base quantity — one of the seven quantities from which all others are built: length, mass, time, electric current, thermodynamic temperature, amount of substance and luminous intensity.
Base unit — the unit of a base quantity: the metre, kilogram, second, ampere, kelvin, mole and candela.
Derived unit — a unit built from base units, such as the newton, .
Estimate — a value found from rounded numbers, used to check that an answer is reasonable.
Half-range — the convention in which the uncertainty of repeated readings is half the range.
Homogeneous — describing an equation whose two sides have the same base units.
Mean — the sum of the readings divided by the number of readings; the best estimate of the true value.
Order of magnitude — the nearest power of ten to a value.
Percentage uncertainty — the absolute uncertainty divided by the value, multiplied by 100%.
Physical quantity — a number together with a unit.
Prefix — a symbol placed before a unit to multiply it by a power of ten, such as kilo for .
Precision — how close repeated readings are to each other.
Random error — an error that changes a reading in an unpredictable way, reduced by repeating the measurement and taking the mean.
Reading uncertainty — the uncertainty of a single reading, equal to half the smallest division of the instrument.
Resolution — the smallest change an instrument can show.
Systematic error — an error that shifts every reading in the same direction, so repeating the measurement does not reduce it.
Uncertainty — the range in which the true value of a measurement is expected to lie.