In physics, scientists make observations, develop theories, experiment and revise their theories. Physics tells us how gravity behaves but does not speak to the origin of gravity's. Instrumentation is one of the active branches in physics. Instrumentation has become a very important subject as an interdisciplinary course in almost all universities. This book is intended as a standard text for the students studying for their under graduation and graduation. A reasonably wide coverage in sufficient depth has been attempted, giving the importance to the basic principles, essential theory and experimental details necessary for understanding the nature, properties and applications of instrument.