An important GPS standard defines the standard reference temperature for all dimensional measurement and all other GPS standards refer to it.

The standard temperature for geometrical product specification and verification is fixed at 20 ºC.

What does this mean for the designer, the manufacturer and the dimensional metrologist?

For the designer:

• all dimensions and tolerances on the drawing apply to a component that is at a temperature of 20 ºC
• if component normally operates at a higher temperature the designer will need to correct the desired sizes at this higher temperature to
  20 ºC for the drawing
  

For the manufacturer:

• during manufacture the component must be measured close to 20 ºC,
  
• how close to 20 ºC depends on the materials and the tolerances involved.
  

For the dimensional metrologist final inspection will either be made:

• in a temperature controlled room at 20 ºC
  
• by comparison with known artefacts of similar material at a temperature close to 20 ºC
• by a measuring machine that measures the component temperature and makes appropriate corrections
• by the operator making the measurement at some other temperature and making manual corrections

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Good practice online modules

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• Dimensional
• Overview of basic design and interpretation of an engineering drawing
• An introduction to datum
• An introduction to geometric tolerancing
• An introduction to the designer's role when designing a component
• An introduction to the manufacturer's role when designing a component
• An introduction to the inspector's role when designing a component