7. Conclusion

Pressure is one of the most frequently measured quantities. It is characterized by its breadth and diversity. Today's standards and calibration methods make it possible to disseminate the pressure unit throughout the industrial sector, with appropriate measurement uncertainties.

However, due to the absence of a high-performance primary standard in the low-pressure range, unmet needs in terms of uncertainties are regularly raised in this pressure range. National metrology institutes are working on new primary standards based on fundamental laws or constants of physics, in particular an optical method consisting of measuring variations in the refractive index of helium in gaseous form. Eventually, transfer standards based on this measurement principle are likely to equip metrology laboratories.