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1、外文资料LevelRodsandLenelsTherearemanykindsoflenelrodsavailable.Someareinonepieceandothers(foreaseoftransporting)areeithertelescopingorhinged.Levelrodsareusuallymadeofwoodandaregraduatedfromzeroatthebottom.Theymaybeeitherselfreadingrodsthatarereaddirectlythroughthetelescopeortarget
2、rodswheretherodmansetsaslidingtargetontherodandtakesthereadingdirectly.Mostrodsserveaseitherself-readingorastargetrods.AmongtheseveraltypesoflevelrodsavailablearethePhiladelphiarod,theChicagorod,andtheFloridarod.ThePhiladelphiarod,themostcommonone,ismadeintwosections.Ithasarear
3、sectionthatslidesonthefrontsection.Forreadingsbetween0and7ft,therearsectionisnotextended;forreadingbetween7and13ft,itisnecessarytoextendedtherod.Whentherodisextended,itiscalledahighrod.ThePhiladelphiarodisdistinctlydividedintofeet,tenths,andhundredthsbymeansofalternatingblackan
4、dwhitespacespaintedontherod.TheChicagorodis12ftlongandisgraduatedinthesamewayasthePhiladelphiarod,butitconsistsofthreeslidingsection.TheFloridarodis10ftlongandisgraduatedinwhiteanredstripes,eachstripebeing0.10ftwide.Alsoavailableforeaseoftransportationaretapesorribbonsofwaterpr
5、oofedfabricwhicharemarkedinthesamewaythataregularlevelrodismarkedandwhichcanbeattachedtoordinarywoodstrips.Onceajobiscompleted,theribboncan,beremovedandrolledup.Thewoodstripcanbethrownaway.Theinstrumentmancanclearlyreadthesevariouslevelrodsthroughhistelescopefordistancesupto200
6、or300ft,butforgreaterdistanceshemustuseatarget.Atargetisasmallredandwhitepieceofmetalattachedtotherod.Thetargethasavemierthatenablestherodmantotakeareadingtothenearest0.001ft.Iftherodmanistakingthereadingswithatargetandifthelineofsightofthetelescopeisabovethe7-ftmark,itisobviou
7、sthathecannottakethereadingdirectlyinthenormalfashion.Therefore,thebackfaceoftherodisnumbereddownwardfrom7to13ft.Thetargetissetatacertainmarkonthefrontfaceoftherodandasthebacksectionispushedupward,itrunsunderanindexscaleandavernierwhichenablestherodmantotakethereadingonthefront
8、.Beforesettinguptheleveltheinstrumentmanshouldgivesome
