in describing preferred embodiments of the present invention illustrated in the drawings , specific terminology is employed for the sake of clarity . the invention , however , is not intended to be limited to the specific terminology so selected , and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose . in that form of the preferred embodiment of the present invention chosen for purposes of illustration , fig1 and 2 show system 100 operable with water conduit c , such as a potable water supply line for a public water system , comprising supply line c s and outlet line c o . system 100 preferably includes first conduit 110 , first electromagnetic fluid flow meter 120 , second conduit 130 , second electromagnetic fluid flow meter 140 , and flow control valve 150 . system 100 is preferably operable with water supply pipeline c to determine and record a net volume of water flow therethrough via measuring a rate of flow of the water . in operating the system in connection with a main water line , such as found in a typical municipal water system , it has been found that electromagnetic fluid flow meters sold by siemens as model nos . 8000 or 5100 may be useful as fluid flow meters 120 and 140 , but many other commercially available mag meters may be useful and are well known in the art . system 100 may further be operable with a control device ( not shown ) that receives one or more output signal from each of first and second electromagnetic fluid flow meter 120 , 140 , as is known in the art . as will be understood by those skilled in the art , an indication of one or more of net volume of water flow , instantaneous water flow rate , average water flow rate , peak water flow rate , or the like may be provided locally by system 100 or remotely , such as via an electronic communication network . mag meters are currently commercially available that may be configured to provide downloadable data logging information that may be monitored for data relating to a specific date and time . such meters can typically be configured for wireless communication so that data may be accessed remotely , saving substantial time and expense in reading and checking the meters . further , the meters may be configured to provide some type of warning or error message should the meter fail to operate properly . second conduit 130 is preferably installed in - line with the water supply pipeline c . as such , a first proximate end of second conduit 130 may be in fluid communication with supply line c s , and a second distal end of second conduit 130 may be in fluid communication with output line c o . thus , it is generally preferred that second conduit 130 be approximately the same size and shape as water supply pipeline c . second electromagnetic flow meter 140 may be operationally employed within second conduit 130 to measure the rate of flow therethrough , and flow control valve 150 may be disposed downstream from second flow meter 140 . optionally , adjustable length conduit 160 may be disposed between second conduit 130 and supply conduit c s , to assist in adjoining the compound mag meter into the intended section of water supply pipeline c . it should be understood that when second conduit 130 is said to be “ connected to ” or “ in fluid communication with ” water supply pipeline c s , such connection may or may not include adjustable length conduit 160 . first conduit 110 is preferably in operable fluid communication with water conduit c at a location upstream of second electromagnetic fluid flow meter 140 and flow control valve 150 , such as via joint 111 . connecting joint 111 may be formed as a tapped joint , a saddle joint , a molded joint , or via any conventional fluid conduit connection means and / or techniques . similarly , first conduit 110 may , alternatively , be operable with water conduit c via second conduit 130 , such as where adjustable length conduit section 160 is not included , wherein joint 111 is defined as the intersection of first end 113 of first conduit 110 and second conduit 130 . in any event , first end 113 of first conduit 110 is preferably located at a distance from second electromagnetic flow meter 140 sufficient to reduce an effect on a metering accuracy of second electromagnetic fluid flow meter 140 associated with turbulence or flow irregularities potentially caused by first conduit 110 . first conduit 110 preferably includes adjustable - length conduit section 170 and first electromagnetic fluid flow meter 120 disposed in - line , i . e . in serial connection , therewith , whereby any water flow through first conduit 110 is preferably measured , recorded , and / or processed by first electromagnetic fluid flow meter 120 . for such purpose , first electromagnetic fluid flow meter 120 may include an on - board register , or may be operable with a remote register or processor . as with adjustable - length conduit section 160 , discussed above , adjustable - length conduit section 170 , may be replaced with one or more fixed - length conduit section , or may be omitted entirely , such as in new installations of process conduit . first conduit 110 is preferably further operable with water conduit c at a location downstream of second electromagnetic fluid flow meter 140 and flow control valve 150 , such as via joint 115 connecting flow control valve 150 and second end 117 of first conduit 110 . thus , first conduit 110 preferably acts as a bypass conduit around second electromagnetic fluid flow meter 140 and flow control valve 150 , whereby water may flow through process fluid conduit c when flow control valve 150 is closed . in a preferred potable water supply application , first conduit 110 preferably comprises a conduit formed of a suitable material , such as ductile iron , cast iron , polyvinyl chloride , or the like , having an internal diameter of approximately 1 ″. accordingly , a conduit section associated with first electromagnetic fluid flow meter 120 preferably likewise has an internal diameter of approximately 1 ″. as should be understood , however , first conduit 110 and a conduit section associated with first electromagnetic fluid flow meter 120 may be selected to have other cross - sectional shapes and / or sizes . first conduit 110 may preferably further include valves 119 , for example disposed proximate first end 113 and second end 117 , whereby maintenance of first conduit 110 and / or first electromagnetic fluid flow meter 120 may be performed without shutting off flow through process fluid conduit c . first electromagnetic fluid flow meter 120 preferably includes a power source 125 , such as in the form of a battery , a solar - power generator , and / or the like , whereby adequate electrical power may be supplied for normal operation of first electromagnetic fluid flow meter 120 when electrical service is unavailable , such as due to remote location , power failure , or the like . in such normal operation , first electromagnetic fluid flow meter 120 preferably creates a magnetic field that induces an electrical current in the fluid disposed within first conduit 110 . a sensor device of first electromagnetic fluid flow meter 120 , such as a pair of electrodes , is preferably operable to output a signal corresponding to an electrical potential between the electrodes . first electromagnetic fluid flow meter 120 , or , alternatively , a remote control device or register , is preferably operable to determine a value of the velocity of the water within first conduit 110 based on the output signal of the sensor device . the determined velocity value may be recorded , and / or used to compile a water consumption value , approximately equal to a total volume of water flowing through first conduit 110 during a relevant period of time . second electromagnetic fluid flow meter 140 is preferably configured in an analogous manner as first electromagnetic fluid flow meter 120 , and is preferably adapted to operate with a larger diameter conduit . in one exemplary and non - limiting embodiment , second conduit 130 has an internal diameter approximately six times greater than the internal diameter of first conduit 110 . thus , in the preferred potable water supply application described above , second conduit 130 preferably comprises a pipe formed of a suitable material and having an internal diameter of approximately 6 ″. accordingly , in the preferred potable water supply application , supply conduit c s and outlet conduit c o preferably likewise comprise pipes formed of suitable material and each having an internal diameter of approximately 6 ″, whereby use of system 100 in fire prevention supply lines is enabled . it should be noted , however , that although the preferred ratio of the cross - sectional area of second conduit 130 to the cross - sectional area of first conduit 110 is approximately 6 : 1 , the ratio may be as great as approximately 10 : 1 , or more , and may be as small as approximately 1 : 1 . the size of the conduits is limited only by the availability of mag meters suitable to measure anticipated flow rates in said conduits . one advantage of mag meters in large diameter pipe applications is that the cost of mag meters does not rise proportionally to the size of the pipe as is the case with turbine meters . it has been found that compound mag meters designed for 6 ″ water pipelines may be manufactured for about the same cost as compound meters using mechanical flow meters , and that compound mag meters designed for 8 ″ pipe may be produced even more cheaply than comparably sized mechanical compound turbine meters . the sizes selected for the first and second conduits , 110 , 130 , may influence the selection of the first and second flow meters 120 , 140 and the configuration of flow control valve 150 . in the described configuration , first flow meter 120 is intended to measure lower anticipated flow rates , and second flow meter 140 the higher anticipated flow rates . flow meters should be selected that provide acceptable accuracy at the flow rates anticipated for the selected pipe diameters . in addition , the flow meters should preferably have a “ crossover range ”, that is , a flow range at which the two meters are about equally accurate at measuring flow rates . this “ crossover range ” is where flow control valve 150 should be designed to allow flow through second conduit 130 . as shown in greater detail in fig2 , flow control valve 150 preferably comprises generally planar member 153 hingedly operable with an interior of conduit section 151 via hinge 155 . generally planar member 153 is preferably biased in a first position , shown in fig2 , wherein generally planar member 153 sealingly engages projection 157 proximate a peripheral portion of generally planar member 153 . thus , generally planar member 153 may prevent backflow of water , i . e . flow of water from outlet conduit c o to supply conduit c s , when in the first position . generally planar member 153 preferably further prevents downstream flow through second conduit 130 when a water pressure downstream thereof is less than a water pressure upstream thereof by an amount less than a predetermined threshold , referred to as the cracking pressure . when the upstream water pressure exceeds the downstream water pressure by an amount greater than the cracking pressure , generally planar member 153 preferably swings about hinge 155 to allow water to flow therepast . it is important to note that a shape and contour of projection 157 is preferably selected to reduce turbulence or flow irregularities caused by water flow therepast . additionally , hinge 155 is preferably operable to allow generally planar member 153 to open quickly once the cracking pressure is exceeded , whereby transition period may be reduced , and flow rates in second conduit 130 reach levels for which second electromagnetic fluid flow meter 140 is accurate in a short period of time . furthermore , a distance between second electromagnetic fluid flow meter 140 and projection 157 is preferably selected to reduce the affect of any turbulence caused by projection 157 and / or generally planar member 153 on the accuracy of second electromagnetic fluid flow meter 140 . finally , the diameter of each of supply conduit c s , second conduit 130 , and outlet conduit c o , is preferably selected to reduce turbulence therewithin associated with typical maximum flow rate values expected based on the application . nonetheless , other flow control devices , including alternative valves , or the like , may be utilized , which facilitate realization of the advantages of the preferred flow control valve 150 . an additional advantage mag meters have over other types of meters is that they can measure flow rate in both directions through a pipe . one can take advantage this operational property by making the compound metering system of the present invention self - testing . this can be a significant advantage to municipalities that are required to test in - line water meters on a regular basis . the self - testing procedure may be used without hiring third party companies or purchasing expensive equipment , which may result in significant savings in operational cost . referring now to fig3 , one preferred embodiment of the present invention is shown that enables one to practice such a self testing procedure . the system in fig3 is similar to that shown in fig1 , with a primary difference being the addition of a removable plug 200 in the first conduit 110 . removable plug 200 may be located upstream from first flow meter 120 . to administer the flow test , one should first close a line isolation valve downstream from c 0 so that water does not flow downstream from the metering system . the total forward flow for second flow meter 140 and the total reverse flow for first flow meter 120 should be recorded . then both of valves 119 a , 119 b may be closed , to stop flow in the first conduit 110 . removable plug 200 may then be removed , and a hose attached to direct water flow to a desired location , such as the ground , or , preferably , a measuring vessel of some sort so that water flow amounts may be verified . the downstream valve within the first conduit 119 b may then be opened . this will allow water to flow forward through second flow meter 140 , and then reverse through first flow meter 120 , through the hose , and , optionally , into the collection vessel . the two flow meters should register the same flow rate at this point . the flow meters may then be calibrated as may be necessary to reflect the appropriate flow rate . the flow rate may be cross - checked by directing the water flow into a graduated vessel of appropriate size , and checking the amount of time taken to fill the vessel . as described in the preferred potable water supply application , system 100 is preferably operable to measure flow rates and totalize flow volumes at flow rates from one half gallon per minute to ten thousand gallons per minute . furthermore , the maximum error tolerance of the preferred embodiment is approximately 2 %. thus , revenue generated by water metering can be dramatically increased due to a reduction in the total volume of unaccounted water . additionally , savings may be achieved by decreasing the pumping cost of maintaining adequate pressure in the potable water distribution system . accordingly , it is contemplated that numerous conventional compound meter systems may be replaced with compound meter systems according to the present invention . therefore , numerous methods are contemplated for using and / or making a compound meter system according to the present . of course , further flow rate variation and / or greater error tolerance could be applied without departing from the scope of the present invention , and while continuing to provide the benefits thereof over conventional systems . for example , in one method , one or more component ( s ) of system 100 may be supplied separately or in a disassembled state . the one or more component ( s ) may then be retrofit into an existing compound meter system , such as when one or more components thereof wear out or break , or at another time when replacement is desired . over time , each component of the existing compound meter system may be replaced by components of system 100 . as mentioned above , such retrofit may be facilitated by one or more of adjustable length conduit sections 160 and 170 , such as in the form of extendable conduit sections , interchangeable sections of different lengths , mutually - engageable modular sections , or the like , whereby first and / or second conduit 110 , 130 , may engage existing fittings or conduit sections . alternatively , system 100 may be supplied in a pre - assembled state , wherein wholesale replacement of an existing compound meter system is simplified , or for use in new installations . furthermore , system 100 may be provided in a sealable pit enclosure . finally , system 100 may be provided in a custom format to facilitate convenient replacement of existing meters . for example , where a compound meter system of given dimensions needs to be replaced , system 100 may be manufactured to include substantially similar dimensions , whereby installation of system 100 into an existing potable water distribution network may be simplified , such as by eliminating the need to modify the existing supply conduit and outlet conduit . as will be understood by those ordinarily skilled in the art , where , as in the preferred embodiment shown and described , both fluid flow meters are formed as electromagnetic fluid flow meters 120 , 140 , account may be taken of any electrical current induced in first conduit 110 and second conduit 130 by a magnetic field created by second electromagnetic fluid flow meter 140 and first electromagnetic fluid flow meter 120 , respectively . alternatively , shielding , sequential creation of magnetic field , or other precaution may be taken to prevent first electromagnetic fluid flow meter 120 from inducing an electrical current in second conduit 130 , and vice - versa . additionally , although the preferred embodiment includes two electromagnetic fluid flow meters , alternative numbers of flow meters and respective associated conduits and flow control valves , such as three or more flow meters and conduits . as will further be understood by those ordinarily skilled in the art , and as discussed above , system 100 may be formed as a unitary device , whereby incorporation thereof in a process fluid conduit may be simplified . such a unitary device may include permanent or removable connections between first conduit 110 and second conduit 130 and between conduit section 151 and first conduit 130 , or may include seamless transitions therebetween . as such , system 100 may be provided in a fully assembled state , in a partially assembled state , or in a completely disassembled state . while reference to such a potable water supply conduit is made in the disclosure , it should be understood that system 100 may be implemented in any conduit carrying a conductive fluid , including but not limited to liquids having dissolved substances , liquids carrying suspended matter , slurries , or the like . having thus described exemplary embodiments of the present invention , it should be noted by those skilled in the art that the within disclosures are exemplary only and that various other alternatives , adaptations , and modifications may be made within the scope and spirit of the present invention . accordingly , the present invention is not limited to the specific embodiments as illustrated herein , but is only limited by the following claims .