the apparatus shown in fig1 has a spool holder 1 , on which a conical mounting tube 2 is placed , through which a coaxial drive shaft 3 extends , which is joined in a rotationally fixed manner with a hollow , substantially l - shaped flyer arm 4 . yarn 11 is removed essentially tangentially from the spool 10 ( fig2 ). the drive shaft 3 is rotatably supported at 5 and is joined in a rotationally fixed manner with a stepping motor 6 , secured to the spool holder 1 , via a gear 600 . the flyer arm is balanced at its end with a counterweight 601 . a small low inertia measuring wheel 7 ( fig1 and 3 ) is rotatably supported on the end of the flyer arm 4 , forming a sensing means for the supply speed of the pulled - off yarn , and is coupled via a shaft with a tachometer generator 9 that is also located on the flyer arm 4 . instead of the tachometer generator 9 , an angle code reader or some other pulse transducer can also be used . the yarn 11 arriving from a spool 10 mounted on the mounting tube 2 in a rotationally fixed manner travels to the circumferential surface of the measuring wheel 7 , which is spaced apart from the spool 10 , viewed in the direction of yarn travel . the yarn is looped in several adjacent windings around the cylindrical circumferential surface of the measuring wheel 7 , the number of loops being such that the measuring wheel 7 is coupled with the yarn 11 in a slip free manner . the yarn 11 that leaves the measuring wheel 7 is guided by three run - out eyes 16 , one of which is stationary and preferably located coaxially with the drive shaft 3 . between the two run - out eyes 16 , the yarn 11 that is running out is scanned by the feeler arm 18 of a run - out shutoff device 13 attached to the flyer arm 4 . the yarn emerging from the third run - out eye 16 is delivered to a yarn consumer , not otherwise shown . in the area between the spool 10 and the measuring wheel 7 , the yarn 11 travels via a yarn tensioning roller 22 ( fig4 ) which is mounted on a lever arm 23 which is pivotably supported on the flyer arm 4 at 24 and is loaded with a tension spring 26 , which is supported at one end on the flyer arm 4 . the initial tension of the tension spring 26 at any given time is selectively adjustable by a screw 25 . as shown in fig4 in the normal operating situation the yarn tensioning roller 22 is mounted in such a way that on its way from the circumferential surface of the spool 10 to the circumferential surface of the measuring wheel 7 , the yarn 11 undergoes a deflection from the straight connecting line . by means of this deflection , a yarn reserve is formed , which in accordance with fig4 can be used up by pivoting the lever arm 23 clockwise about the pivot axis 24 . a guide bracket 8 secured to the flyer arm 4 assured reliable yarn guidance in the vicinity of the measuring wheel 7 of the tensioning roller 22 . as shown in fig3 the tachometer generator 9 coupled with the measuring wheel 7 is equipped , via a line 30 , a switch 31 the function of which will be explained below , and a line 32 , with a data evaluation and distribution circuit 33 , to which an output signal in the form of an analog voltage is supplied by the tachometer generator 9 . this output signal is representative of the yarn travel speed . for electrical connection between the tachometer generator 9 and other electrical device disposed on the flyer arm 4 , as well as the electronic circuit shown in fig3 and located in a fixed location on the spool holder 1 , slip rings 12 provided on the drive shaft 5 are used . connected to the output side of the data evaluation and distribution circuit 33 , via a line 34 , is a voltage / frequency converter 35 , which converts the analog output signal of the tachometer generator 9 , which may have been amplified in the data evaluation and distribution circuit 33 , into a pulse train the pulse frequency of which is representative of the yarn travel speed . this pulse output signal 36 is supplied via a line 37 to a control circuit 38 , which on the output side is connected via a line 39 to the stepping motor 6 . connected to the voltage / frequency converter 35 via a line 40 is a display device in the form of a display 41 , to which the pulse output signal 36 of the tachometer generator 9 , which represents the yarn travel speed , is accordingly delivered , and which digitally displays the value of the yarn travel speed at any given time . this display can be provided on one side of the spool holder 1 . via the line 40 , a coupling device , in the form of a plug device 42 , for external signal lines is supplied by the the voltage / frequency converter 35 with the pulse output signal of the tachometer generator 9 ; it is thereby possible to evaluate this signal outside the yarn supply apparatus as well , which will be explained in detail further below . a computer 44 is connected via a line 43 with the data evaluation and distribution circuit 33 or optionally with the voltage / frequency converter 35 ; the computer 44 makes it possible to store and / or monitor data supplied via the line 43 and to emit an output signal that is representative of the given data , or of the results of monitoring , to a line 47 leading to the display 41 , so that the corresponding data can be displayed there . a selector switch 48 located between the lines 45 , 46 and 47 enables various outputs of the computer 44 to be triggered selectively . the wiper 50 of a potentiometer , schematically shown at 49 in fig3 is connected to the pivot axis 24 of the lever arm 23 . this potentiometer emits a signal representing the angular position of the lever arm 23 , and thus representing the location of the tensioning roller 22 , via a line 51 , which is connected to a regulator 52 , which contains a command value transducer and is connected via a line 53 to the control circuit 38 . electric current is supplied to the individual portions of the circuit by means of a power pack 54 , the power supply line of which is shown at 55 and the current supply lines of which , leading to the individual parts of the circuit , are identified as 56 - 58 . the supply of electric current to the data evaluation and distribution circuit 33 is effected via a line 59 and a switch 60 , which is mechanically coupled to the tensioning roller 22 . two supply lines 61 , 62 carrying supply voltages of opposite polarity are connected to the switch 60 , so that from the polarity of the supply voltage present on the line 59 , the data evaluation and distribution circuit 33 can recognize the position of the switch 60 . initially , it is assumed that the yarn demand of the yarn user is zero . the yarn supply apparatus assumes the position shown in fig1 . the yarn is under tension ; the magnitude of the yarn tension is determined by the adjustment of the tensioning 26 . when the yarn user begins to remove yarn , yarn is removed via the run - out eyes 16 . thus the measuring wheel 7 is set into clockwise rotation , as shown in fig1 and the yarn reserve formed by the yarn tensioning roller 22 is reduced or partially consumed . once the measuring wheel 7 begins to turn , the tachometer generator 9 emits an output signal , via the line 30 , that is proportional to the yarn travel speed ; this signal is delivered by the data evaluation and distribution circuit 33 to the voltage / frequency converter 35 . there the analog output signal is converted into a stepping pulse signal having a corresponding stepping frequency , which is also proportional to the yarn travel speed . this pulse output signal 36 is then delivered , via the control circuit 38 and the line 39 , to the stepping motor 6 , which drives the flyer arm 4 at a speed corresponding to the yarn travel speed . each of the pulses proceeding from the control circuit 38 to the stepping motor 6 can correspond to either one full angular increment , or merely a portion of the angular increment , of the stepping motor 6 . at the same time , via the line 43 , the computer 44 receives the data pertaining to the yarn travel speed , which is either stored in the computer or used to generate an output signal , which via the lines 45 , 47 and the switch 48 , which is in the position shown in fig3 reaches the display 41 , where it is displayed . regardless of how the yarn removal by the yarn user takes place chronologically , the stepping motor 6 thus drives the flyer arm 4 at a speed associated with the quantity of yarn being supplied at that time , the magnitude of this speed being determined by the measuring wheel 7 . in this manner , via the tachometer generator 9 and the stepping motor 6 as well as the circuit portions 33 , 35 , 38 located between them , the measuring wheel 7 is rigidly synchronized electrically with the stepping motor 6 . it can thus be seen that the control loop is formed by : the measuring wheel 7 and the tachometer generator 9 coupled thereto ; line 30 and circuits 33 , 35 , 38 and line 39 ; motor 6 and shaft 3 , to which the flyer arm 4 is coupled ; alternatively , the flyer arm may be stationary and the spool can be coupled to the motor ; the yarn 11 itself , which is coupled in slip - free manner to the measuring wheel 7 . the yarn closes the control loop . no external command operating speed / actual yarn operating speed comparator and associated controller is used in this loop . the magnitude of the tension at which the yarn is delivered to the user is determined by the adjustment of the spring 26 . once yarn consumption stops , the speed of the measuring wheel 7 drops accordingly , and hence the speed of the stepping motor 6 and thus of the flyer arm 4 is reduced as well , until finally the apparatus has come to a stop . even when the machine is at a stop , the yarn remains tensed at the predetermined value by means of the spring - loaded yarn tensioning roller 22 that acts on the yarn between the spool 10 and the measuring wheel 7 . the size of the yarn reserve formed by the yarn tensioning roller 22 varies when the yarn supply speed varies . it can be kept constant via the potentiometer 49 and the regulator 52 . the potentiometer 49 emits a signal via the line 51 which is representative of the position at any given time of the position of the tensioning roller 22 and thus of the size of the yarn reserve present between spool 10 and the point where the yarn arrives at the measuring wheel 7 . in the regulator 52 , this signal is compared electrically with a command value . the result is a signal , corresponding with the deviation , if any , traveling via the line 53 to the control signal 38 , which by correspondingly varying its output variable , which is emitted via the line 39 , causes the stepping motor 6 to rotate about an angular value such as to compensate for the deviation . since the regulation is integral , the deviation disappears . the magnitude of the yarn tension that is established can be monitored by a separate tension feeler 69 , which via the line 70 emits a corresponding measurement signal to the data evaluation and distribution circuit 33 , which is turn passes a corresponding datum on to the computer 44 . a datum representing the yarn tension can be interrogated at the output line 46 via the switch 48 and then displayed on the display device 41 . if when the machine shuts off the yarn tension of the yarn supply apparatus becomes zero (&# 34 ; o &# 34 ;), for instance because a sagging loop of yarn forms , or if it drops below a predetermined lower threshold , then the yarn tensioning roller 22 is pivoted by the spring 26 into a threshold position , in which the switch 60 coupled with the lever 23 is actuated via this lever . this reversal has the result that via a control line 101 , a pulse transducer 100 that emits pulses of constant pulse frequency via a line 102 is switched on , and that the data evaluation and distribution circuit 33 , via the voltage / frequency converter 35 , furnishes a reversal command for the stepping motor 6 to the control circuit 38 . supplied with the pulses of the pulse transducer 100 , the stepping motor 6 is started up in the rotational direction opposite the direction of yarn supply . thus the flyer arm 4 begins to rewind the hanging loop of yarn , and continues this until such time as the yarn , as it becomes tenser , again returns the yarn tensioning roller 22 far enough toward its normal position that the switch 60 switches back into its normal position and the pulse transducer is switched off , as soon as the yarn is again in its normal position . instead of the spring 26 , the yarn tensioning roller 22 can naturally also be loaded with an adjustable weight , an electromagnetic force , or a force generated in some other way . it is also possible for the tension feeler 69 to be combined directly with the yarn tensioning roller 22 , that is , to use the yarn tensioning roller 22 itself , or the device generating the force coupled with it , for measuring the yarn tension . in the described embodiment , the output signal of the tachometer generator 9 -- after appropriate signal conversion and amplification -- controls the stepping motor 6 directly . alternatively , the synchronizing between the stepping motor 6 and the tachometer generator 9 can also be done in such a manner that the output signal of the tachometer generator 9 is used as a command value , to which a servo regulator included in the control circuit constantly regulates the speed of the stepping motor 6 . the yarn run - out monitor , which with its feeler arm 19 scans the yarn 11 that is running out , actuates the switch 31 via its feeler arm 18 such that if the yarn breaks , on the one hand the output signal line of the tachometer generator 9 is interrupted , thus instantly stopping the stepping motor 6 , and on the other hand a stop signal is sent to the yarn user via a line 72 . this stoppage of the yarn supply is effected whenever the run - out feeler bracket 18 assumes the position shown in broken lines at 18a in fig4 . the coupling device 42 , finally , makes it possible to supply signals representing the yarn tension and / or the yarn travel speed to a central , external display device or to a central regulating device , which affect the unwinding operation , if necessary , by controlling the electronic control circuits 38 . the control commands can likewise be delivered to the voltage / frequency converter 35 , and thence to the electronic control circuit 38 , via the coupling device 42 . as shown in fig1 , the entire apparatus is in the form of a compact unit . a manually actuated switch 31a makes it possible to selectively reverse the direction of rotation of the drive motor 6 briefly , via a line 73 . in fig5 a modified embodiment of the apparatus is shown , which corresponds in its essential parts and its essential function to that shown in fig1 - 4 . identical elements are therefore identified by identical reference numerals , and so the mode of operation need not be described again . in addition to the embodiment of fig1 - 4 , in the embodiment of fig5 a second stepping motor 6 &# 39 ; is mounted on the spool holder 1 . via a gear wheel 200 , this stepping motor 6 &# 39 ; drives a gear wheel 201 , which is rotabably supported by means of a bearing 201 on the drive shaft 3 and is coaxial thereto ; the mounting tube 2 is coaxially secured on the gear wheel 202 . the second drive motor formed as the stepping motor 6 &# 39 ; makes it possible to rotate the spool 10 in the opposite direction from the flyer arm 4 . as the spool diameter decreases , in other words , the speed of the flyer arm 4 must become correspondingly greater in the embodiment of fig1 - 4 , if the yarn pull - off speed is to be kept constant . this may be undesirable , for mechanical reasons or with a view to the centrifugal and inertial forces that arise , if the speed of the flyer arm 4 drops below a predetermined threshold . by appropriately driving the spool 10 , the speed of the flyer arm 4 can be kept constant , or be kept below a predetermined threshold , for instance at a constant yarn pull - off speed . in principle , the second stepping motor 6 &# 39 ; is capable of driving the spool 10 at a constant speed ; however , it is preferable for the drive by the stepping motor 6 &# 39 ; to be effected such that when the spool 10 is full , the spool is driven slowly , and as the spool diameter decreases the spool drive speed increases , as a predetermined ratio to the speed of the flyer arm 4 . it is also possible for the spool 10 not to be driven along with the flyer arm until beyond a predetermined spool diameter ; the flyer arm 4 revolves alone , until this spool diameter is attained . the circuitry provided for controlling the second stepping motor 6 &# 39 ; is shown in fig6 : the data evaluation and distribution circuit 33 emits a corresponding output signal , via a line 34 &# 39 ;, to a second voltage / frequency converter 35 &# 39 ;, which in turn emits a pulse output signal 36 &# 39 ; via a line 37 &# 39 ;. this pulse output signal 36 &# 39 ; is delivered to a programmable computer 205 , which is also connected at one input to the stepping pulse line 39 of the first stepping motor 6 and which from this line receives stepping pulse signals representing the speed of the first stepping motor 6 and thus of the flyer arm 4 . from the data delivered to it , the computer 205 calculates the pulse count required for the speed of the second stepping motor 6 &# 39 ; corresponding to the spool diameter at a particular time , and via a line 206 delivers a corresponding output signal to a second control circuit 38 &# 39 ;, which via a line 39 &# 39 ; in turn delivers the stepping pulses to the second stepping motor 6 &# 39 ;. instead of and / or in addition to the signal representing the speed of the first stepping motor 6 , a signal representing the yarn quantity pulled off the spool 10 could also be delivered to the computer 205 ; from this signal , the computer can then calculate the diameter of the spool 10 at that time automatically . alternatively , it would also be possible to scan the spool diameter and to supply the computer directly with a signal of this kind , representing the spool diameter . thus the computer 205 is capable of controlling the second stepping motor 6 &# 39 ;, via the control circuit 38 &# 39 ;, as a function of the spool diameter . if need be , this may be done in addition to a speed - dependent control , for instance such that until a predetermined spool diameter is attained or possed , the variation in the speed of the second stepping motor 6 &# 39 ; is effected as a function of the speed ratio with the flyer arm 4 and then as a function of the spool diameter . in a simple embodiment , the arrangement may be such that the spool drive speed is at a fixed ratio to the flyer drive speed .