There has long been debate over how to treat dimensionless quantities, or quantities with the unit one, within the International System of Units (SI). These arguments have been brought into sharper focus because of the increasing application of metrological principles in areas such as chemistry, biology and nanoscience where counting measurements are common. This has caused debates about how the SI should address counting quantities and the unit one (symbol 1). This article reviews the types of quantities with the unit one, how these quantities may be expressed together with their uncertainty and how this relates to counting. The qualities of counting quantities are explored in more detail and the range of possibilities for dealing with the unit one for counting are discussed. It is proposed that the SI should allow only the unit one for counting, but that downstream of the SI there may well be benefits from standardising the use of more descriptive, technical area specific ‘units’ for expressing the results of counting. As with all measurement it is essential that a full description, in words, of the counting quantity being expressed accompanies the measurement result.

关于如何在国际单位制 (SI) 中处理无量纲量或使用单位 1 的量，长期以来一直存在争论。由于计量原理在诸如化学、生物学和纳米科学等计数测量很常见的领域中的应用越来越多，这些论点已成为人们关注的焦点。这引起了关于 SI 应该如何处理计数数量和单位 1（符号 1）的争论。本文用单位一回顾了数量的类型，这些数量及其不确定性如何表达，以及这与计数有何关系。更详细地探讨了计数数量的质量，并讨论了处理计数单位的可能性范围。建议SI应该只允许单位1进行计数，但是在 SI 的下游，标准化使用更具描述性的技术领域特定“单位”来表达计数结果可能会带来好处。与所有测量一样，测量结果中必须对所表达的计数量进行完整的描述。