This Code provides the determination of the weight rate of flow of particulate matter carried in a gas stream confined in a duct or stack. This is accomplished by (a) Measurement of average weight concentrations of particulate matter in the gas stream, and (b) Determination of total gas flow rate. Data thus obtained may be utilized for such purposes as the performance evaluation of gas cleaning apparatus systems, compliance testing in conjunction with emission control and performance regulations promulgated by regulatory agencies, etc. This Code prescribes methods for measuring the average weight concentration of particulate matter carried in a gas stream. Measurement on any other basis (e.g., particle count, dust spot, opacity, etc.) is outside the scope of this Code. Also outside the scope of this Code is the measurement of particle size distribution. This Code also includes supplementary information on (a) Design and selection of sampling trains; (b) Sampling probes and particulate-matter collection apparatus; (c) Particulate-matter sampling systems; (d) Filtration efficiency of filters for fine particulate matter; (e) Sampling in low-velocity gas streams; (f) Particulate-matter collection and the effect of condensed SO3 ; (g) Typical gas-velocity and particulate-matter concentration profiles; (h) Methods of determining number and location of sampling areas; (i) Instrumentation for determining gas velocity; (j) Design and construction of field operating graphs; (k) Graphs and Tables of useful data; and (l) SI System for units of measurement.