fig1 shows an automatic meter reader which has two main parts , a conventional chart recorder 10 that has been modified to incorporate a digitizer 12 and chart pen adaptor 18 . the chart recorder 10 may for example be a dri - flo ii ( tm ) chart recorder , or an itt barton model 202a or 208a differential pressure recorder , but this invention is not restricted to the particular chart recorder , and may be used on a variety of chart recorders and other meters that have a movable arm . as shown in more detail in fig2 and 4 a - 4 c , the chart recorder 10 has three mechanically actuated movable arms 14 a - 14 c which are mounted on pivot points 25 a - 25 c within a housing 15 , in which is installed a backing plate 24 . the backing plate 24 is installed in conventional manner . each movable arm 14 a - 14 c terminates in an indicator tip which includes a pen tip 16 a - 16 c and pen adaptor 18 a - 18 c respectively . ink reservoirs 29 a - 29 c lying on the movable arms 14 a - 14 c respectively in conventional fashion provide ink through ink capillaries 31 a - 31 c respectively to the pen tips 16 a - 16 c respectively . the chart pen adaptors 18 a - 18 c are located at the end of each movable arm 14 a - 14 c respectively . the chart pen adaptors 18 a - 18 c may be each an electromagnetic coil 27 as illustrated in fig5 having an open core through which the pen tips 16 a - 16 c extend respectively into contact with chart paper 20 during operation . the electromagnetic coils 27 may be glued , crimped or otherwise fastened to the movable arms 14 a - 14 c . the inner movable arm 14 c has an angled pen tip 16 c , e . g ., at 45 ° to the vertical , to allow it to fit with the other pen tips 16 a , 16 b . the chart recorder 10 illustrated senses gas flow through a dry gas flow sensing assembly 22 connected via a line 30 to a well . in response to gas flow ( or other parameter being sensed ) in a line ( or other device ) being monitored , the indicator tips 16 a - 16 c move through a range of positions , typically an arc , in response to the meter sensing the physical parameter . the chart 20 rotates about a spindle 32 in the meter 10 . each movable arm 14 a - 14 c follows a different arc across the chart in close proximity to each other . digitizer 12 is mounted on the meter 10 by fitting the digitizer 12 into an opening 26 in the backing plate 24 of the meter 10 . the digitizer 12 has a digitizing grid 28 positioned adjacent the indicator pen tips 16 a - 16 c for sensing the position of the indicator pen tips 16 a - 16 c . digitizing grids themselves are well known , and any of various types may be used in the operation of the invention , although the one selected may require modification to fit into a particular meter . in addition , the digitizing pen typically used with a conventional digitizer is replaced by one or more of the chart pen adaptors 18 a - 18 c mounted on the movable arm of the meter 10 . the digitizing grid 28 may be affixed to the chart backing plate 24 in any of various ways , such as by being held by screws . the chart pen adaptors 18 a - 18 c transmit signals to the digitizing grid 28 in known manner . conventional digitizing electronics and modified conventional programming detects the pen adaptor positions from the meter 10 and converts the pen adaptor positions into an electrical signal representative of the pen position or into a digital format . a cordless , electromagnetic tablet digitizer incorporating a grid and controller such as the mutoh america pen system available from mutoh america inc . of phoenix , ariz ., may be used as the digitizer 12 . there are numerous digitizers that may be adapted for mounting on a chart recorder in accordance with this invention , such as the summasketch ( tm ) digitizer available from summagraphics corporation of seymour , conn ., or the ud - series graphic tablet available from wacom technology corporation of vancouver , wash . the conventional digitizer 12 is provided with the pen adaptors 18 a - 18 c to fit the movable arms 14 a - 14 c and modified shape to fit the backing plate 24 . the digitizer has built in programming which may be suitably modified to suit the particular application . for example , the psc5m ( tm ) or psc6 ( tm ) pen system controller products of mutoh america may be used . as contained in the mutoh america chart pen , the signal from the pen adaptors 18 a - 18 c may be frequency encoded to contain pen switch information ( pen up or down , as well as side switch states ). the digitizer 12 may incorporate a conventional rs - 232 communications port or conventional removable memory card slot 34 . other data interface devices may be used , including a transceiver for remote reading and interrogation of the digitizer 12 . the digitizer 12 acquires data by sensing the position of the pen adaptors 18 a - 18 c on the meter 10 . the digitizer 12 has particular application to circular chart recorders used to determine fluid flow . as shown in fig1 the chart backing plate 24 is replaced or modified to include an opening 26 to contain the digitizing grid 28 which may be etched on to a printed circuit board or screened on a mylar ( tm ) grid or other device . in the mutoh america digitizer , the amplitude and frequency of the received signal on individual sensor grid lines contain the information required to determine pen location , switch status and pen pressure . the system may be retrofitted to existing recorders or enhance newly produced or rebuilt chart recorders with the ability to log the data as it is created . the device can also be applied to indicating instruments and chart recorders of the strip chart or drum variety and digitize the pen positions for any of the variables indicated or recorded . there should be no metal between the pen adaptors 18 a - 18 c and digitizing grid 28 if an electromagnetic coil is used as the pen adaptor 18 a - 18 c . the pen adaptors 18 a - 18 c may be passive or active ( powered ). if the pen adaptors 18 a - 18 c are powered then the power is supplied in the conventional manner from the digitizer 12 along wires that are themselves conventional but are adapted for this invention by running the wires along the movable arms 14 a - 14 c . in some applications , only a single movable arm 14 a , with single pen adaptor 18 a and pen tip 16 a is required . the invention may be readily adapted to any number of movable arms . the digitizer 12 is programmed to sense the pen or indicator positions on the meter 10 and process those signals into time stamped , digital data that can be stored and made available to other devices through the interface 34 . the meter 10 may also be an instrument that just indicates rather then record ( such as pressure gages , speedometers , etc .) in this instance , the indicator tip is a non - marking indicator . the digitizer 12 includes conventional digitizer features such as memory for data storage and power circuitry for low power operation with an external battery pack . resolution of the position of the pen may be chosen to suit the application , but may for example be 1016 points per inch , with 0 . 01 inch accuracy in the vertical position of the pen or 0 . 02 inch in the 45 degree position . the digitizer 12 , when used with more than one pen indicator , may poll the pen indicator positions one pen at a time , each uniquely identified as separate pens . by reading two pens in a gas recorder , wherein both differential pressure and static pressure were measured , would be enough to allow calculation of the gas flow , provided the temperature was manually input or otherwise entered into downstream gas volume calculation software . a person skilled in the art could make immaterial modifications to the invention described in this patent document without departing from the essence of the invention that is intended to be covered by the scope of the claims that follow .