The primary focus of this book is flow measurement. It provides the reader with complete knowledge about various topics related to the subject. It covers a variety of topics ranging from basic theories to applications in microflows and encompasses all the problems related to the phenomenon. It also discusses the numerical and analytical aspects of evaluation of biphasic flow like separation of different phases to perform its independent evaluation and other experimental techniques. The book describes various developmental experiments and machines used for the gas flow, principally combustible gases and air. Lastly, it demonstrates topics on the theological and experimental ways of evaluating 'flow measurement' and that too with the means of pressure changes, applied on large and small flows.