. The Bell System technical journal . E. E., Vol. No. 2., Fel)., 1924. 382 BELL SYSTEM TECHNICAL JOURNAL plete testing equipment is available, by means of which, a largevolume of transmission testing in central offices and private branchexchanges can l)e done in the most convenient manner. Tests usingthese instruments can be made as readily on the transmission circuitsin machine switching offices of both the step by step and panel types asin manual offices. The ear balance set of Fig. 24 requires no ex-ternal source of direct current power and only a three dry cell batteryis required f
. The Bell System technical journal . E. E., Vol. No. 2., Fel)., 1924. 382 BELL SYSTEM TECHNICAL JOURNAL plete testing equipment is available, by means of which, a largevolume of transmission testing in central offices and private branchexchanges can l)e done in the most convenient manner. Tests usingthese instruments can be made as readily on the transmission circuitsin machine switching offices of both the step by step and panel types asin manual offices. The ear balance set of Fig. 24 requires no ex-ternal source of direct current power and only a three dry cell batteryis required for operating the oscillator. It is, therefore, used to thebest advantage in testing private branch exchange switchboards andmagneto .switchboards where the power necessary to operate visualtypes of sets is not readily available. The visual type of set of Fig. 25 is pariicularK- suited lor testingin the larger common battery central offices since it i)ermits measure-ments to be made more quickly and acrnrate1\- than in the caso of the. Fig. 26 ear balance sets. Tiiese larger oftices also ha\e readih axailablethe 24-\lo found wiilithis transmission tostinj; e(|uii)nKnt tlu- followiiij; lal)lr shows a Irouhlt^-classitication which is particularly useful in ^ testing resultsand instigatini; any riHiiiircd romedial iiHisuns. Classijicalion of Troubles Found Ph\sicai defects. Wroni; l\ pe of i>(|iiipiiUTit or Opens. circuit. (irounds. Missini; e<iiiipnienl. Crosses. High resistance. Cut Outs. Low insulation. Hlectrical <lefects. Wrong routing. Incorrect wiring. Bridged conductors. The above classification includes all of the common types of troubleswhich, if not kept out of th
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