Precision

Precision is the degree to which repeated measurements or observations of the same quantity yield the same results under unchanged conditions. It reflects the reproducibility and consistency of measurements. Precision is not the same as accuracy, which describes how close a measurement is to the true value. A set of measurements can be highly precise but not accurate if they are consistently biased, or accurate but not precise if they vary widely.

In measurement science, precision is typically quantified by the spread of repeated measurements, using statistics such as standard deviation, variance, or the coefficient of variation. Instrument resolution, measurement technique, and environmental or operator factors all influence precision. The term is also connected to the instrument’s stated repeatability and to the smallest detectable change, sometimes called resolution.

Two related concepts are repeatability and reproducibility. Repeatability refers to precision under the same conditions over a short time, while reproducibility extends to different conditions, operators, or equipment. Ensuring high precision often involves calibrating instruments, controlling environmental variables, and standardizing procedures.

In computing and numerical analysis, precision denotes the number of significant digits used to represent a value, such as single or double precision floating-point formats. Finite precision can introduce rounding errors and affect numerical stability.

Practical examples illustrate the idea: measuring a length with a ruler marked in millimeters yields lower precision than using a caliper with hundredth-millimeter resolution. In all contexts, improving precision aims to reduce the scatter of repeated measurements and to increase confidence in reported results.