GB/T 29024.3-2025 "Particle size analysis - Single particle optical sensing methods - Part 3: Light extinction liquid-borne particle counter" applies to measuring the particle size and number concentration of particles ranging from 1 μm to 100 μm suspended in liquids. It specifies the measurement, calibration, and verification methods for light extinction liquid-borne particle counters. The standard defines core technical indicators such as particle size setting error, counting efficiency, and resolution, and regulates the error requirements for sampling flow rate, time, and volume. It covers equipment calibration intervals, testing procedures, and report contents, making it applicable for pharmaceutical cleanliness evaluation and the detection of particle characteristics in various liquids. The standard provides a unified framework for the quantitative analysis of particles in liquids, ensuring the repeatability and comparability of test results.