General The testing protocol is limited to single-phase Newtonian fluid flow@ and no consideration is given to pulsation effects. Further revisions of this document may include the testing of such meters in wet gas or multi-phase service and the effects of pulsation. This standard does not address testing protocols of those devices that operate on the principle of critical or choked flow condition of fluids. The testing protocol covers any flow meter operating on the principle of a local change in flow velocity caused by the meter geometry@ giving a corresponding change of pressure between two reference locations. There are several types of differential pressure meters available to industry. It is the purpose of this standard to illustrate the range of applications of each meter design and not to endorse any specific meter. The basic principle of operation of the flow measuring devices follows the physical laws relating to the conservation of energy and mass for the fluid flows through the device. Any API MPMS document addressing a specific type or design of differential pressure flow measuring device will supersede the requirements of this document for that type or design. An example of such standards are all parts of API MPMS@ Chapter 14.3@ Concentric@ Square-Edged Orifice Meters.