High Quality Content by WIKIPEDIA articles! A thermodynamic instrument is any device which facilitates the quantitative measurement of thermodynamic systems. In order for a thermodynamic parameter to be truly defined, a technique for its measurement must be specified. For example, the ultimate definition of temperature is "what a thermometer reads". The question follows - what is a thermometer? Let's assume that we understand mechanics well enough to understand and measure volume, area, mass, and force.