ISO 1:2022

Overview

ISO 1:2022 - Geometrical product specifications (GPS) - defines the concept of a reference temperature and fixes the standard reference temperature for specifying geometrical and dimensional properties. The standard sets the value of the standard reference temperature to 20 °C (ITS-90) and clarifies its role when defining size, location, orientation (including angle), form and surface texture of a workpiece. It also applies to the definition of the measurand used in verification and calibration.

Key topics and requirements

• Standard reference temperature: The normal reference temperature for GPS is t = 20 °C, expressed on the International Temperature Scale of 1990 (ITS-90).
• Reference temperature concept: Distinguishes between a general reference temperature (a specified uniform temperature of an object) and the internationally agreed normal reference temperature.
• Applicability: The temperature applies to geometrical and dimensional properties (size, position, orientation, form, surface texture) and to measurands for verification/calibration.
• Measurement and uncertainty: Where verification occurs at temperatures different from 20 °C, appropriate thermal corrections or uncertainty accounting are required. Specifying a non‑normal reference temperature can increase measurement uncertainty because most dimensional measuring instruments and gauges are calibrated with measurands defined at 20 °C.
• ITS-90 clarification: ISO 1:2022 clarifies that 20 °C is the ITS-90 value; the ITS-90 approximation differs from thermodynamic temperature by about 2.8 mK at 20 °C, which for steel amounts to roughly 0.03 µm per meter - negligible for most work but relevant for high‑level calibration.

Practical applications and who uses it

ISO 1:2022 is essential for anyone involved in dimensional metrology, including:

• Design engineers and CAD modelers specifying tolerances on drawings and product documentation
• Quality engineers and inspectors performing dimensional verification
• Calibration laboratories and metrology service providers defining measurands and calibration conditions
• Manufacturers of dimensional measuring equipment and gauges
• Standards committees and technical writers aligning GPS requirements

Typical uses:

• Specify the reference temperature on technical drawings and CAD files
• Define measurand conditions for calibration certificates
• Apply thermal corrections or include temperature-related components in measurement uncertainty budgets
• Ensure instruments are calibrated and reported relative to the 20 °C reference

Related standards

• ISO 14638 (GPS matrix model) - situates ISO 1 within the broader GPS framework
• ISO/IEC Guide 99 (VIM) - terminology for metrology
• ISO/IEC Guide 98-3 (GUM) and ISO/TR 16015 - guidance on uncertainty and thermal effects

Keywords: ISO 1:2022, standard reference temperature, 20 °C, ITS-90, geometrical product specifications, GPS, measurement uncertainty, calibration, dimensional metrology, thermal expansion.