Applies to measurement of air flow for compressors and exhausters. Section Two deals with the measurement of air flow by means of a nozzle in the pipeline, normally on the delivery side of a compressor or on the inlet side of an exhauster. Section Three deals with the measurement of air flow on the inlet side, using a conical intake; this method is suitable for large air flows or where it is otherwise incovenient to use the nozzle specified in Section Two.