Purpose of this work is to explain pressure and all aspects which are connected to that subject. It is described through six chapters, starting from where pressure is formed and the way its use has changed and developed throughout history. Besides that, types of pressure are described in detail considering that measuring pressure has changed and was perfected with time in mind, measuring instruments and methods are also described which were used long time ago and those which are used nowadays. In this work the importance of measuring pressure with precision and correctness in mind is also described, the same importance is applied to converting pressure so in this work the pressure converters are described in depth. This work is concluded with the part which consists of an explanation to how pressure is applied and used on board ships and its sole importance to functionality of a ship which can be considered as a complex system,. In the conclusion, which can be found at the end of this work, the importance of pressure and the measuring of the same with precision in mind can be understood and also be applied in every day’s use, starting from mechanical systems and machines to a human’s health.