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CCU/CCQM Workshop on “The metrology of quantities which can be counted"

28 to 30 March 2023

CCU-CCQM Workshop

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The CCU/CCQM Workshop on quantities which can be counted will be held from 28th to 30th March 2023 as an online-only meeting. Free registration is now open using the online registration links above. The meeting will consist of plenary sessions on 28th to 30th March 2023. An outline of the current program is available in the “Working Documents” section below. The full workshop agenda will be provided shortly.

Quantification based on counting, either of single entities or of quantized processes and other phenomena, is of increasing importance in metrology. This is because scientific and technical progress requires measurements to be made with an ever-increasing accuracy and sensitivity at very fine spatial resolutions or on extremely short timescales. Quantum technology is approaching and, the needs of industry, health care, and the environment are requiring ever lower detection limits in chemical and biological measurement. All this points towards counting as the preferrable, or even inevitable, way for measurement results to be sensitive and accurate enough for their intended use in future.

Closely related to this, the specific aspect of the new definition of the mole that has attracted great attention is its dependence on a number of entities – new for a definition of a base unit. It raises the question of if and how counting and number-based quantities can be integrated into the SI where measurements are usually conducted by comparing sizes of continuous quantities. This forces metrology to explain in more detail the consistency of its established system of units in a quantized world.

The SI brochure already acknowledges the relevance of quantities that cannot be described in terms of the seven base quantities of the SI but have the nature of a count. Those quantities are described as quantities with the associated unit one. This guidance may be interpreted in a number of ways and raises the question of if and how the unit for quantities that are counted is recognized and realized within the SI system. The issue is further complicated by special names often being used for the unit one. The lack of specific guidance in this area is potentially far reaching. It is not yet clear if the result of such quantities can and should be expressed in terms of the SI and whether the notion of traceability to the SI extends to these quantities. This also applies to the question of which communities and consultative committees should take responsibility for standardizing measurements for such quantities.

Key topics

The workshop will include three sections:

  • Concepts and theoretical aspects of counting and the unit one
  • Counting entities (case studies from electricity, mass, chemistry and biology)
  • Counting processes & other phenomena (case studies from radioactivity to light)


The objectives of this workshop are:

  • to trigger a discussion on counting and number quantities across the metrological community so that a common understanding of counting is achieved
  • to prepare proposals for a clear delineation between
    • kinds of quantity that can only be expressed as a count
    • kinds of quantity where counting is involved in the measurement, but results are expressed not as a count
    • kinds of quantities not involving counting
  • to give guidance for:
    • a clearer nomenclature for counted quantities
    • a better metrological understanding of counts and their traceability
    • where the responsibility for providing traceability for such quantities lies

Steering Committee

Bernd Güttler


Richard Brown


Pavel Neyezhmakov


Robert Wielgosz


Michael Stock



Working documents

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