US2393403A - Telephone traffic recording system - Google Patents

Description

Jan. 22, 1946. J. E. OSTLINE TELEPHONE TRAFFIC RECORDING SYSTEM Filed Jan. 22, 1944 16 Sheets-Sheet l mum mwzzvrozz JOHN E. OSTLINE I .BY

ATTORNEY Jan. 22, 1946. J. E. OSTLINE 3 3 TELEPHONE TRAFFIC RECORDING SYSTEM Filed Jan. 2 2, 1944 16 SheetsSheet 2 AIS m INVENTOR. y JOHN E. OSTLINE ATTORNEY I Jan. 22, 1946. J. E. OSTLINE 2,393,403

TELEPHONE TRAFFI C REbORDING SYSTEM Filed Jan. 22, 1944 1a She ets-Sheet 5 FIG. 2A

I u m INVENTOR. 2 8:8; JOHN E. OSTLINE ATTORNEY Jan. 22, 1946. J. E. OSTLINE TELEPHONE TRAFFIC RECORDING SYSTEM Filed Jan. '22, 1944 1a Sheets-Sheet 4 Ea vfi kmflo MNO Ev p L. 8m. mnn vma m5 mam m N G h 3 mum , mmvmx JOHN E OSTLINE ATTORNEY- Jan. 22, 1946. J. E. O'STLINE TELEPHONE TRAFFIC RECORDING SYSTEM Filed Jan. 22, 1944 16 Sheets-Sheet 5 SEE E 595 m QE INVENTOR. JOHN E. OSTLINE ATTORNEY 2, 1946'. J. E. OSTLINE TELEPHONE TRAFFIC RECORDING SYSTEM Filed Jam. 22, 1944 16 Sheets-Sheet 6 INVEN TOR. JOHN E. OSTLINE ATTORNEY Jan. 22, 1946. .1. 5., OSTLINE TELEPHONE TRAFFIC RECORDING SYSTEM Filed Jan. 22, 1944 16 Sheets-Sheet 7 CABLE TO PRINTER FIG. 9

IN VEN TOR. JOHN E. OSTLINE ATTORNEY Jan- 4 Y J. E. OSTLINE TELEPHONE TRAFFIC RECORDING SYSTEM Filed Jan. 22, 1944" 16 Sheets-Sheet 8 CABhE TO PRINTER FIG.9

INVENTOR! JOHN E. OSTLINE TTORNEY Filed Jan 22, 1944 16 Sheets-Sheet 9 a 6E mmhzEa Oh M 5.

INVENTOR. JOHN E. OSTLINE ATTORNEY 16 Sheet-Sheec 10 JOHN E. OSTLINE J. E. OSTLINE Filed Jan. 22, 1944 'IELEPHONE TRAFFIC RECORDING SYSTEM Jan. 22, 1946.

0 3w mm? w wmm TE A o M j 0 0 0 0 8 80 mm 3 m6 m oE. m3 u n T|J.| m E x m v H FHN O NV. L aw 1 66 M 2w L 03 5:8 1 mwwi .6 n M6 66 u I n f6 5 03 u 8 919: .32 u a ww m2: .8 0mm m m 2.? -w wwsm 6T :8 unm Emmnm mat mEzEm q. 8w 2b in 5 MU oh H 3 ATTORNEY Jan. 22, 1946.

E. OSTLINE 2,393,403

TELEPHONE TRAFFIC RECORDING SYSTEM 16 Sheets-Sheet 11 Filed Jan. 22, 1944 TERMINAL IKOOK CABLE TO I PRINTER nae INVENTOR. JOHN E. OSTLJNE ATTORNEY Jan. 22, 1946,

J. E. OSTLINE TELEPHONE TRAFFIC RECORDING SYSTEM Filed Jan. 22, 1944 16 Sheets-Sheet 12 JOHN E. OSTLINE ATTORNEY Jan. 22, 1946. J. a. OSTLINE 2, TELEPHONE TRAFFIC RECORDING SYSTEM Filed Jan; 22, 1944 16 Sheets-Sheet l3.

INVENTOR. JOHN E. OSTLINE ATTORNEY .Jan. 22, 1946. I osT 2,393,403

I TELEPHONE TRAFFIC RECORDING SYSTEM RECORDING CHART FIG. I2 A O|2345167895520123456789i30l23456789H30l23456789i550|23456789i; 7 J3 42 00 000000 80 0 0 00000 0.00000000' 0 0000 0 00 O0 9 00 0000000 0 0 000000 00'0000000O 0000 0 000 0 9 l5 0 0 0 00 0 000 000 000 0040 0 I 005.... .05. lo 90 I5 0 0 0 0 0 000 000 0 0 00 0 00 00 .0 0005 lo 00 3o 0 0 0 0 000 000 0 0 0 0 0 lo 00000 00000 '00000 00 00 0 0H .00 00 0 000 |0 IO 00 30 FIG. I20 1 Ol23456789 Ol234567 89 Ol234250123456789 0|23456789 M23425? 7 I3 42 0000000000 000 0 0 I500 00000 0 0 0 0 0 0 0' 9 46 0o 0000000000 000 0 0 v '500 00000 0 0 0 0 0 0 0' 9 46 0000 0000 0000 0 0 0 0 '0 .l 7 I0 00 I5 0000 0000 0000 0 0 0 0 00000 00 00000000 0 0' 00.30 0000 0000 0000 0 0 0 0 300000 00 00000000 0 I0 00 45 OI23456789 Ol23456789 0123456789 O l23456789 023456789551 L; I3 42 0.000000 0 000000 00000 '0 000 000000 00000 0 lo 00 I5 0 00000000 000000 Y 00000 0 000000000 0 00 .4 6 IO 00 3O 0 00000000 000000 00000 0 000 000000 00000 0 IO 00 45 INVENTOR.

JOHN E. OSTLINE i Y BY ATTORNEY I J. E. os'rLnyE TELEPHONE TRAFFIC RECORDI NG SYSTEM Jan. 22, 1946.

Filed Jan. 22, 1944 16 Sheets-Sheet 1e 7 FIG :3 J

, RUNK TERMINAL PINS TRAFF ER INVENTOR. 7 JOHN E. osrum: Z Z

Patented Jan. 22, 1946 TELEPHONE Tame RECORDING SYSTEM John E. stline, Chicago, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, III., a corporation of Delaware Application January 22, 1944, Serial No. 519,251

42 Claims. The present invention relates ingeneral to traflic recording equipment for telephone, or like,

systems and, more particularly, to improvements in apparatus for automatically testing and recording at regular intervals the busytrunks in one or more trunk groups associated with theapparatus.

One 01 :the principal operating and maintenance requirementsin automatic-telephone systems is that of knowing the volume of traflic for which the trunks and switches are to be provided. As a telephone exchange or network increases in size, or as various classes of trafilc change from one period to another, it becomes necessary to addto, subtract from, or re-arrange existing switching and trunk equipment to meet these changing traffic conditions. Therefore, periodic trailic studies become a necessary routine for trailic engineering purposes.

Methods of obtaining information relative to the duration and amount of .calls in each trunk and switch group in the busy hour have varied from time to time. The most obvious method is, of course, that of observing the traffic manually by means of a stop watch. It is seldom used, due to the relative slowness with which representative amounts of observations can be accumulated.

Another method of obtaining holding time measurements is by recorders which mechanically and electrically indicate the holding time of each call in a group of switches or trunks during a certain time interval. These recorders, of which there are several types, usually have one common feature consisting of a paper tape moving at a pre-determined speed on which the length and the amount of :calls are indicated by means of recording pens. The chief disadvantage with all devices of this typevresides in the fact that the records obtained are of no use until considerable time and laboris expended in measuring, interpreting and summarizing the recorded results into fundamental quantities, and

even then these results will beinfiuenced-by some guess work and errors due to manual interpretations.

In order to overcome the, disadvantage and limitations of the foregoing methods, and to make possible arapid accumulationqof fundamental trafiic data on a considerable amount of calls, a method referred tofas .switch counts" has for a number of years been used. This method consists of placing one or more-trunk groups an observer who counts and records at fixed regular intervals the amount of switches held in an operated or busy condition. Such data, when obtained in suflicient quantities, will indicate the average load in any switch or trunk group and by a relatively simple formula the unit calls carried by the trunk group can thus be obtained. This figure once having been ascertained, a consultation of standard tramc tables will indicate whether a group needsadjusting or it it is satisfactory for handling the ofiered traflic.

As in the case of mechanicallytape recorded data, this second method of obtaining traflic data, by manual observation has a number of disadvantages. The principal one of these is that the human element is always a variable factor and in addition the effectiveness of this method depends upon the frequency and regularity of each scanning operation, that is, the counting of busy switches during each period. In order to obtain this information correctly and in order to cover as many trunk groups as possible at the same time, many observers may be required. It. is also found desirable to not only record the amount of trunks busy in the group, but also to identify the particular trunks which are busy. This information is desirable in order to determine if the observed graded" groups are properly distributed or if they need re-aclJusting.

It is an object of the present invention to provide an improved unit of apparatus, whereby switch counts are made, added and recorded automatically. This unit of apparatus hereinafter referred to as Trafilcorder, scans each trunk group under observation at regular fixed intervals. The data obtained from each scanning is then stored, analyzed and recorded in printed form comprising numeral characters.

This data can, without any further analyzation or prolonged study, be used to ascertain if a trunk group or groups under observation requires any re-adjustment or not.

Another object of the invention is to provide an improved automatic testing-and recording apparatus, which is operated to record in printed numerals a printed record designating, or identifying, each trunk and its idle or busy condition at periodic pre-determined timed intervals, the number of trunks in each trunk group and the number of such trunks which arebusy at given pre-determi'ned timedlintervals, the date and time and the total number 01 busy trunks in each to be studied under manual visual observation by 56 trunk group for a period oftime comprising a pre-determined numberof' the periodic timed .number of :trunks arranged in one or more groups.

Another object of the invention is to provide circuits and apparatus to print a typewritten record comprising a heading," a plurality of periodic trunk recordings, and a total recording. The heading comprises numerals and spacings designating the number of trunk groups, the number of trunks in each group, the identity of each trunk ineach group and the day, month and year, The periodic trunk recordings comprising successive lines printed at pre-determined timed intervals, each line identifying each busy trunk and designating the number of busy trunks in each trunk group and the time of day.

The total recording is printed after the periodictrunk recordings and shows the total sum ofthe busy trunks in each of the trunk groups during the periodic trunk recording operations.

Further novel features believed to be characteristic of the invention are set forth in the following description andin the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figs. 1A and 1B illustrate the wiring ar-' rangements of the three scanning switches Al,

A2 and A3, and their associated controlling relays H10, H0, I20, the gang group relays GRI and GRZ and a portion of the storage relays SR. Figs. 2A and 2B, and 3A and 3B illustrate similar scanning switche Bl, B2 and B3 and Cl, C2 and C3 and their associated control relays; Fig. 33 also diagrammatically represents three adders which are similar to the N0. adder shown in Fig. 4B; Fig. 4A illustrates the No. 1 adder and Fig. 4B the No. 5 adder; Fig. 5 illustrates the timing apparatus comprising an hours switch EU, a tens minute switch MT, a units minute switch MU, and a seconds switch SE and their associated relays and a time panel for displaying the time of day; ,Fig. 6 illustrates the primary switch PS together with its control relays and start key K2.

Fig., .'7 illustrates the wiper controlled by the manually controlled keys shown in. Fig. 11, the

time pulse unit'l50 and the cross connecting terminal block 195; Figs. 8A and 8B illustrate the two counter switches LA and LB and their associated control relays; Fig. 9 illustrates thewiring arrangement of the recordprinterand Fig. 10 diagrammatically illustrates the mechanism of the record printer; Fig. 11 shows the time lamp panel, the manually controlled keys comprising the date keys K3, K4, K5 and K6, the grouping keys K1, K8, K9, KIO, Kl l, Kl2, KM, KN, Kl5 and KIB, the group selecting key Kl, the start key K2 and the minutes and hours keys MK and HK; Figs. 12A, 12B, 12C and 12D show in part the kind of recording charts printed by the apparatus; and Fig. 13 shows a perspective view of this unit of apparatus, referred to as a Tramcorder.

Referring now more particularly to the drawings, the scanning switches are of the well-known rotary switch type which operate their wipers one step in response to the release of their associated stepping magnets. Each scanning switch has six wipers, the first one for controlling the stepping circuits, the second for controlling the circuits and apparatus to print the headings, such as shown in Figs. 12A, 12B, 12C and 12D, the 3rd and 4th for controlling the circuits and apparatus to print the second and successive lines on the recording charts, the 6th for controlling the circuits to operate the adders to total the numher of busy trunk conditions encountered, and the 5th for controlling the circuits and apparatus to print the total busy trunk conditions added by the adders and shown in the last line on each recording chart. Trunk terminal pins 0 to 49, inclusive, shown at the extreme right of Fig. 1B, are cross connected by means of jumpers to the test conductors of the trunks to be tested. The ganggroup relays GR! and GR2, when energized, connect these trunk test conductors to test conductors T0 to T49, inclusive. The storage relays SRO to SR49 are individually connected to corresponding ones of these test conductors and are operated if the corresponding trunk test conductors are grounded due to the corresponding trunks being busy. The test conductors T0 to T49, inclusive, terminate in the bank contacts accessible to the fourth wiper 01' each scanning switch and these wipers are connected by way of conductor 654 to the primary switch PS (Fig. 6) for controlling Mark relay 510.

The second wiper of each scanning switch has access, by way of its bank contacts, to printer conductors P9 to P9, inclusive, extending by way of a cable to the printer magnets shown in Fig. 9. The second wipers of the scanning switches also have access to conductors extending by way of a cable to Fig. 7 to the wipers of the grouping keys and these scanning wipers are connected by way of conductor 652' to the primary switch PS in Fig. 6.

The third wiper of each scanning switch has access to conductor BI'I extending to the primary switch relay group (Fig. 6) and to conductors extending to the counter switches for controllin the operation. of the printer. Some of these wipers have access to conductors extending to the time switches shown in Fig. 5. These wipers are connected by way of conductor 653 to the primary switch PS. y

The sixth wiper of each scanning switch is connected by way of conductor 656 to primary switch PS and has access to conductors extending to the adders for stepping the adder switches one step for each, busy trunk encountered. The fifth wipers of the scanning switches are connected by way of conductor 655 to the primary switch PS and have access to conductors extending to the adders for reading the total added b the adders.

The adders shown in Figs. 4A and 4B, and diagrammatically shown by squares in Fig. 313, each comprise two rotary stepping switches of the well-known type and a group of control relays. The switches HA and HC are stepped one step for each busy trunk encountered by the scanning switches, while the switches HB and HD are stepped one step for each busy registrations. These switches have access to printer conductors extending in a cable to the printer magnets shown in Fig. 9.

The time switches HU, MT, MU and SE in Fig. 5 are of the well-known rotary type switches which step their wipers on the deenergization of their respective stepping magnets. One wiper of each of these timing switches is connected by way of a cable to the scanning switches shown in asaa os conductors extending by way of a cable to the printer magnets shown in F18. 9. Another set of wipers of these time switches are connected to the lamps in the time lamp panel for displaying the time of day. Relays Bill, 520 and 530 are proyided for switching over to the proper tens hour printer conductor. Time switch HU is pro- 1 vided with oil-normal springs 53 which are in normal open position when the wipers of the units hour switch .HU are in their first position. These off-normal springs close when the wipers tactwith the rotating roller I029. Cam I028 instantly turns through one-half revolution, and in so doing, actuates the type bar I03! to print the numeral '9. Each cam, such as "128, is pivof this switch take their first step. The hours 1 key HK and the minutes key MK corresponding 1 to the hours key, HK and the minutes key MK shown in Fig. 11 are provided for manually setting the time switches to correspond to the time of day.

Fig. 6 shows the primary switch PS and associated control relays. The primary switch P8 is of the well-known rotary type which steps its wipers on the deenergization of its stepping magnet. The start key .K2, corresponding to ke K2 in Fig. 11, is provided for initiating the operation of the Trafllcorder after the time switches, the month and day keys, and the grouping keys have been properly set,

Fig. 7 shows a plurality of key wipers controlled by the manually set corresponding keys in Fig, 11 and a time pulse unit 150 which is operative when ground is connected thereto for transmitting time pulses every seconds. The key wipers are connected by conductors extendingby way of a cable to the scanning switches and these wipers have access to printer conductors extending by way of a cable to the printer magnets in Fig. 9. The key wiper Kl has access to conductors extending to the scanning switches for controlling certain of the scanning control relays in accordance with the desired roupings of the trunks. A terminal block 195 isshown in.

Fig. 7 connected to printer conductors extending to the printer magnets and is arranged for cross connection by means of jumpers to conductors extending to the scanning switches for designating the last two digits of the year.

Figs. 8A and 8B show the counter switches LA and LB which are also of the well-known rotary type. The bank contacts of the counter switches are connected by way of printer conductors to the printer magnets of Fig. 9. Fig. 8A shows a group of counter switch control relays for controlling the operation of the counter switches LA and LB.

Fig. 9 shows the printing magnets and driving motor of the record printer and Fig. 10 shows the mechanism associated with one of these printing magnets. This record printer is an electrically driven typewriter and is commonly known as the Electromatic" printer. Tht Electromatic printer comprises a motor driven typewriter such as disclosed in Product Engineering for November, 1930, and in The Story ofElectromatic," published by the Electromatic Typewriters, Inc., Rochester, New York. During the time the electromatic printers are in use, the small electric motors for controlling the same are in constant operation and are constantly operating the soft rubber rollers, such as roller I029, shown in Fig. 10. In order to operatethe electromatic printer in this case, magnets POM to PQM, inclusive, and mark magnet PMA are added to control the key bars. In Fig. 10 magnet P9M operates its armature I026 to in turn actuate the key bar H121. This results in bringing the cam I028 into con:

oted at one end ofa bell crank forming part of the linkage it operates. Normally, a stop holds eachcam a few thousandths of an inch out of contact with the roller surface, but when the magnet correspondingto a given cam is operated. a spring forces the serrated surface of the cam against the soft rubber-surface of the roller and the two rotate together without slippage. In so doing, the cam pivot and the link to which it is attached are forced away from the roller. this motion, for which the motor supplies the power, that actuates the type bar. Since the mechanical construction of the electromatic printer is not part of thisinvention, it is believed that this general description of its operation will sufiice. Any further details regarding the mechanical operation of this type of printer may be had by referring to the aforesaid publications. All the letter type bars of this printer have been removed and only the numeral type bars 0 to 9, inclusive, and one other type bar referred to as the Mark type bar having a small zero for indicating 'busy trunks remain because only these type bars are used in the present invention. The carriage of the printer moves one step when any type bar is actuated and also steps or spaces when the space magnet PSPM is actuated. The printer is provided with a printer ribbon control magnet PRCM which, when actuated, positions, the red mally opened when the carriage of the printer is in its normal position and closes as soon as the carriage moves in its first step. The printer motor 938 is actuated as long as the conductor- 936 is grounded.

Fig. 13 shows a perspective view of the portable 'Iraflicorder" having a box like enclosure for enclosing the equipment comprising the rotary switches and their associated relays. The combined lamp and key panel and the electromatic printer is shown mounted on the top of this unit.

Along the righthand side of the enclosure are provided trunk terminal pins to which the test trunks of the trunks to be tested are cross connected by means ofjumpers. A pair of battery terminals and a pair of fuses are also shown.

The "Traflicorder is a unit of apparatus which will collect, analyze and record in printed form all data required to ascertain the volume of trafilc carried by each group of trunks under observation. This data is obtained by scanning each connected trunk group for busy trunks every 15 seconds during the busy hour or any other periods for as long a time as may be desired. The Trafficorder is arranged to observe traffic on a maximum of fifty trunks which may be grouped as follows: grouping No. 1 for 5 groups 'of 10 trunks, grouping No. 2 for 3 groups of 16 trunks, grouping No. 3 fora groups of 25 trunks, grouping No. 4 for a single group of 50 trunks.- The foregoing number of trunks in each trunk group are the maximum, and, if desired, the number of trunks in each trunk group may be less for any group.

After connecting the desired trunks to the trunk terminal pins of the Tramcorder and after op- Itls.

erating the manual keys of the key panel are set in accordance with the desired trunk grouping, the minutes and hours keys are operated until the lamp panel displays the correct time of day. The start key K2 is then operated to cause certain of the scanning switches, in accordance with the grouping selected, to operate in a series of scanning cycles, or operations. The selected scanning switches, comprising three in number, are operated through a. complete scanning. cycle every 15 seconds. The first scanning cycle of the scanning switches causes a heading, such as shown in Fig. 12A to be printed across the record sheet. This heading" shows the identity number of each connected trunk, the actual number of trunks in each group, the number of groups, and the month, day and year. After this heading" is printed a second scanning cycle is automatically started and the primary switch PS takes one step to alter the functions performed by these scanning switches. The second and subsequent cycle operations of the scanning switches cause the printing of the second and subsequent lines, such as shown on chart I 2A. Each trunk found busy is identified by a mark. The number of busy trunks in each'trunk group is counted and this total is printed. The clock time of these cycle operations is also printed. During these cycle operations the number of busy trunks in each trunk group are added in the respective adders and after sixty such cycle operations the totals added by the adders are printed on the chart as shown in the last line of Fig. 12A.

Detail operation The first operation to be performed by the observer is to connect the test conductors of the trunks to be observed to the trunk terminal pins shown to the right on Fig. 1B. To do this the observer wheels the Trafflcorder to some distributing frame, or distributing point, and then jumpers only the test conductors of the trunks to be observed to the trunk terminal pins to 49, inclusive, as shown in Fig. 1B. The observer also connects the negative and positive battery bus bars of the exchange battery to the battery terminals on the Tramcorder.

The next operation is to operate the group selecting key KI to select a particular grouping. The Traflicorder is arranged to observe trafflc on a maximum of 50 trunks which can be grouped as follows:

Grouping #1-five groups of ten trunks each, Grouping #2three groups of 16 trunks each, Grouping #3two groups of 25 trunks each, Grouping #4one group of 50 trunks.

The observer now sets the key Kl, shown in Fig. 11, to the number corresponding to the desired grouping. The wipers KI and KI (Fig. '7) are associated with the key KI and are operated to corresponding positions.

Assuming that the ke Kl is operated to its #1 position then the wiper KI is operated into engagement with conductor III in Fig. 7 for theset to their "0" positions. This operation or the keys divides the fifty trunks into five groups of ten trunks each. Referring now to Fig. 7, the wipers KI K8, K9, KM and KM are each set to their second positions in engagement with the Pl conductor which extends to the #1 printer magnet PIM shown in Fig. 9. It should be mentioned that the wipers such as wiper K1 is moved at the same time that the key K1 is manually moved by the observer. In the same manner the wipers, which are shown primed, operate at the same time as the correspondingly indicated key. 'The keys KI2, KI3, KM, KIS and KIG and theircorresponding primed wipers shown on Fig. '1 are each operated to their last positions inengagement with the conductor P0 which extends to the #0 printer magnet POM shown in Fig. 9.

In response to grounding the'conduotor IN, the time pulse unit I50 is operated-to ground conductor I00 every fifteen seconds or four times per minute. The grounding of conductor 10! also completes a circuit for starting the printer motor 938 over a circuit as follows: from grounded conductor IM to the printer motor start conductor 930 included in the printer cable which extends to Fig. 9 and thence by way of conductor 936 to the printer motor 938 to battery. The grounding of conductor I0l also completes a circuit for the printer carriage return magnet PCRM it the carriage of the printer is oiI-normal as follows: from grounded conductor 10!, contact 68! of start relay 660, printer oilfnormal conductor 935 to the printer ofi-normal contacts 931 and to the winding of the printer carriage return magnet PCRM to battery. The operation of the printer carriage return magnet PCRM will return the printer carriage to its initial typing position as well as advancing the recording sheet one vertical spacing step. Grounded conductor IOI also grounds the HU3, the MT3, the MU3, and the SE4 wipers of the time displa switches shown in Fig. 5. Assuming that these wipers at this time are in the position shown in Fig. 5, the grounding of these wipers will complete circuits for the #0 unit hours lamp, the #0 tens minute lamp, the #0 unit minutes lamp, and the #00 seconds lamp shown in the time display panel of Fig. 5.

In the lower portion of Fig. 5 are shown the minute key MK and the hour key HK which are provided for the purpose of directly operating the stepping magnets of the minutes and hours time switches so as to manually set the time display to correspond with the actual time of day the observation is to be taken.

As shown in Fig. 5 the tens minute switch MT and the units minute switch MU are both in 0 position thereby lighting the 0 tens and 0 units minutes lamps. Assuming that the time is 9:45 a. m., the minute key MK is operated forty-five times to operate the stepping magnet 560 of the unit minute switch MU over the following circuit: from grounded conductor 10! thru the spring contacts of the minute key MK and from thence to the winding of stepping magnet 560 to battery. On each deenergization of the stepping magnet 560 the unit minute switch MU operates its wipers MUI, MU2, and MU3 one step. When wiper MUI reaches its tenth position a circuit is prepared for operating the stepping magnet 550 of the tens minute switch at contacts 562. The next time stepping magnet 560 is energized, the contacts 562 completea circuit from the grounded wiper MUI by way of the tenth bank contact to the winding

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