the means for programming the microprocessor the efm 10 also has data output means for retrieving data stored in the rom as shown in fig2 the data output means will include a display screen 24 mounted in a face plate 23 that provides a digital display of current or historical gas flow data stored in the rom the screen 24 is preferably protected by a transparent face plate cover 25 made of glass or plastic the efm 10 features an internal button 26 for activating the display of gas flow data the internal button 26 is accessible only upon removal of the face plate cover 25 an external display button 28 is also provided for activating the display of gas flow data and for additional functions as described later herein as previously indicated the preferred embodiment of the efm 10 includes an mmc card reader writer which permits the use of an mmc card as an additional and particularly convenient data output means as will be described herein it will be readily appreciated by persons skilled in the art that the display screen 24 may be configured in a variety of ways for selective display of different gas flow parameters by way of example the display screen 24 in fig2.