本文件提供了ISO 11171:2020的背景以及使用μ m（c）作为APC颗粒计数数据粒度报告的唯一方法。它还总结了使用SRM 2806d候选材料和参考材料（RM）8632a混悬液进行的重现性国际实验室间研究（ILS）的结果。ILS结果为用于APC主要校准的SRM 2806d的认证提供了依据。本文讨论了它们对颗粒计数和过滤器测试的影响。

This document provides the background for ISO 11171:2020 and the use of μm(c) as the sole means of reporting particle size for APC particle count data. It also summarizes results of the international inter-laboratory study (ILS) of its reproducibility using SRM 2806d candidate material and suspensions of Reference Material (RM) 8632a. The ILS results provided the basis for certification of SRM 2806d used for primary calibration of APC. Their implications with respect to particle counting and filter testing are discussed in this document.