A review is given of the development of boiler-plant instrumentation, from the early use of measuring instruments as mere safety devices to the modern employment of remote centralized control, based upon the comprehensive measurement of the operating conditions.It is contended that, as improvements in plant design and operating efficiency are governed by the degree to which their dependent factors are known and understood, exploratory measurement must embrace all the quantities which are measurable, while the operating measurements must include those of all the variables which are susceptible to regulation. A table of essential measuring instruments for shell-type and water-tube type boilers is included.Remote manual control is then compared with automatic control. The purpose is to show that, as measurement is now the acknowledged basis for control, it follows that the measuring instruments which detect and report the adverse tendencies should be used to institute the corrections needed to arrest them, wherever this is practicable.