A portable flow measuring apparatus measures the speed of sound and/or vortical disturbances propagating in a fluid flow to determine a parameter of the flow propagating through a pipe. The apparatus includes a sensing device that includes an array of pressure sensors, which may be removable, used to measure the acoustic and convective pressure variations in the flow to determine a desired parameter. A portable processing instrument processes the signals provided by the sensing array to provide an output signal indicative of a parameter of the fluid flow. The portable processing instrument includes a processor having appropriate processing algorithms to determine the desired or selected parameter(s) of the process flow 12. The portable processing instrument has a user interface to permit the user to select the parameters to be measured in the process flow, and/or more importantly, to enable the user to modify particular parameters or functions in the processor 30 and/or processing algorithms. The user interface 32 also enables a user to modify the code of the algorithm via a graphic user interface (GUI), keyboard and/or user input signal 34.