SAP 中差异的一些概念

-.z.1.SAP关于本钱的概念2.差异的计算方法.3.实际本钱计算方法4.SAPvariance1.本钱的概念标准本钱=标准价格*标准数量+作业价格*标准数量方案本钱=方案价格*方案数量+作业价格*方案数量

实际本钱=实际价格*实际数量+作业价格*实际数量

目标本钱=标准价格*实际数量+作业价格*实际数量注意在SAP中目标本钱根据生产订单中产品本钱评估时的价格乘以生产订单完工入库量乘以BOM用量的积.方案本钱为生产订单方案生产量乘BOM用量乘方案生产变式中定义的价格.方案本钱即企业本钱方案时使用的本钱，是企业全部方案的一局部。方案本钱同目标本钱的差异是：目标本钱是本钱控制的需要，方案本钱是企业全面预算和方案控制的需要。方案本钱的核算时间为方案订单产生时，当您保存订单时已方案本钱会自动计算，如果您做出的更改与本钱核算有关，则在您保存订单时，会重新计算已方案本钱。

想更新已方案本钱，选择订单功能计算本钱。

要显示预计本钱，选择转向本钱分析。2.差异分算标准改订差〔本期标准本钱－前期标准本钱〕*前期期末库存数量

采购价差〔PO单价－本期标准本钱〕*汇率*本次入库数量

我认为应该是这样的：〔PO单价*汇率－本期标准本钱〕*本次入库数量

应付立帐〔IV〕〔价格差异IPV〕〔发票金额－PO金额〕*汇率

结报汇差〔本期汇率－前期汇率〕*结报外币金额

工单差异〔材料用量差异，工费效率差异〕

工单实际投入金额－工单实际产出金额跨工厂物料异动差异〔转出工厂标准本钱－转入工厂标准本钱〕*本次转拨数量物料帐差异；

PriceDifferent(价差〕：

仅指汇率差以外的差异，包括采购价差，标准改订差，工单差异，工厂转拨差异等

E*changeDifferent(汇差〕：

采购结报时的汇率差异

Single-LevelDifferent(单阶差异〕：

仅指本身所产生的差异

Multi-LevelDifferent(多阶差异〕；

仅指来自下阶料号的差异SAP料号差异合计＝料号起初差异＋来自下阶的差＋标准改订差＋采购差异＋结报价差＋结报汇差＋工单差异＋跨工厂物料异动差异

分摊：期末库存差异数转至其他料件差异数分摊至销货本钱差异数3.实际本钱计算方法在生产订单中实际本钱的计算如下：

1、直接材料本钱：是为生产订单直接领用的物料的本钱，等于本*订单领用物料的数量乘以此物料主数据中的价格，数据来源为MM模块；

2、直接人工费：等于本*订单耗用的实际工时乘以本产品的单位小时人工费率，实际工时在订单确认时输入，单位小时人工费率来自于作业价格，通过工艺路线中的工作中心计算得出，其贷方为对应的本钱中心；

3、制造费用：等于本*订单耗用的实际工时乘以本产品的单位小时制造费费率，实际工时在订单确认时输入，单位小时制造费费率来自于作业价格，通过工艺路线中的工作中心计算得出，其贷方为对应的本钱中心。

实际本钱同目标本钱比照计算差异，以进展本钱控制。4.sapvariancesVariancesontheinputside:ScrapvariancesYouspecifywhetherscrapvariancesarecalculatedinthestepDefineVarianceKeys.Youcontrolwhetherscrapvariancesaredisplayedbyselectingtheindicatorforscrapvariancesinthevariancevariant.Thisenablesyoutocontrolthedisplayofscraporthedeductionofthescrapfromtheactualcostsseparatelyforeachvariancevariant;youcanalsocontrolthisseparatelyforeachvariancevariantbyassigningthevariancevarianttoatargetcostversion.

E*ample:

Youhavespecifiedinthevariancekeythatscrapvariancesaretobecalculated.

Intargetcostversion0,youareusingvariancevariant001.Thescrapvariancesareturnedoninvariancevariant001.

Intargetcostversion3,youareusingvariancevariant999.Thescrapvariancesareturnedoffinvariancevariant999.

IntheValuationVariantforWorkinProcessandScrap(TargetCosts),youcanspecifywhichcostestimateisusedasabasisforcalculatingthetargetcostsforthevaluationofthescrapvariances.Youspecifythisvaluationvariantforscrapintargetcostversion0.Scrapvariancesarecalculatedinalltargetcostversionsinaccordancewiththevaluationvariantspecifiedintargetcostversion0.

Inputpricevariances

Inputpricevariancesarethedifferencesbetweentheplannedpricesandtheactualpricesoftheresourcesused.Ifthisindicatorisset,youshouldmakesurethat:

TheMaterialoriginindicatorissetinthecostingviewofthemasterrecordofcost-criticalmaterials

TheRecordquantityindicatorissetinallrelevantcostelements

Inputquantityvariances

Inputquantityvariancesaredifferencesbetweentheplannedandactualinputquantitiesoftheresources.Ifthisindicatorisset,youshouldmakesurethat:

TheMaterialoriginindicatorissetinthecostingviewofthemasterrecordofcost-criticalmaterials

TheRecordquantityindicatorissetinallrelevantcostelements

Resource-usagevariances

Aresource-usagevarianceariseswhenadifferentresourceisusedthanwasplanned.Remaininginputvariances

Remaininginputvariancesaredifferencesontheinputsidethatcannotbeassignedtoanyothervariancecategoryontheinputside(suchasoverhead).

Variancesontheoutputside:Lotsizevariances

Lotsizevariancesaredifferencesbetweentheplannedfi*edcostsandthechargedfi*edactualcosts.Lotsizevariancescanonlybecalculatedfortargetcostversion0.

Outputpricevariances

Outputpricevariancesaredifferencesbetweenthetargetcredit(atthestandardprice)andtheactualcredit(fore*ampleatthemovingaverageprice).

Mi*ed-pricevariancesIfyouvaluateyourinventorieswithmi*edprices,mi*ed-pricevariancesmayresultifthestandardpricecalculatedonthebasisofthemi*edcostestimateisnotthesameasthetargetcostoftheprocurementalternative.

E*ample:

Supposethestandardpriceforamaterialwascalculatedinami*edcostestimate.ThematerialhaspricecontrolindicatorS,whichmeansthatthegoodsreceiptsarevaluatedatthestandardpriceandtheorderiscreditedaccordingly.Whenthesystemcalculatesthetotalvariance,itparesthecontrolcost(inthiscasetheactualcost)withtheprocurementalternativeforwhichtheorderwascreated.Ifthetargetcostfortheprocurementalternativeisnotthesameasthecreditsatthestandardprice,ami*ed-pricevariancewillresult.

Seealso:NewVarianaceCategory:Mi*ed-PriceVariance

Remainingvariances

Remainingvariancesarevariancesthatcannotbeassignedtoanyothervariancecategory(fore*ample,roundingdifferences).Ifthesystemcannotcalculateanytargetcosts,onlyremainingvarianceswillbecalculated.

Variancesarecalculatedforallvariancecategoriesthatareselectedinthisview.Ifaparticularvariancecategoryisnotselected,thevariancesofthatcategorywillbeassignedtotheremainingvariances.Scrapvariancesareane*ceptiontothis:ifyoudon'twanttoseescrapvariances,thesevariancescanenterallothervariancecategoriesontheinputside.

Ifnovariancecategoriesareselected,onlyremainingvarianceswillbecalculated.

TheMinordifferencesfieldenablesyoutohavesmallamountschargedandsettledasremainingvariances,althoughtheyarestillassignedtotherelevantvariancecategoryinthedetailscreenofvariancecalculation.Actualcost

Indicateswhichactualcostswereallocatedtothecostcenter,businessprocess,order,orcostobjectID.InCostObjectControlling,thepostedactualcostscontain:Workinprocess

Scrap

VariancesWIPIndicatesthecostsforworkinprocessinthechosencolumn.Thiscolumnisnotusedfororderswithfullsettlement.Use

Thevariancecalculationprocesssubtractsthevalueoftheworkinprocessandscrapfromtheactualcosts,andparestheresultingcontrolcostswiththetargetcosts.

DependenciesYoucantransfertheworkinprocesstoFinancialAccountingandProfitCenterAccountingwhenyousettle.InProductCostControlling(CO-PC)

Theunfinishedproductswhosecostsarecalculatedinoneofthefollowingways:BycalculatingthedifferencebetweentheactualcostschargedtoanorderandtheactualcostscreditedtotheorderByvaluatingtheyieldconfirmedtodateforeachmilestoneorreportingpoint,lesstherelevantscrapScrapvarianceUse

Scrapvariancesarecalculatedinthevariancecalculationprocess.Dependencies

ScrapvariancesarevaluatedaccordingtothestrategyspecifiedinCustomizingforCostObjectControllinginthevaluationvariantforworkinprocess(targetcosts)andscrap.Ifyouhavenotdefinedavaluationvariantforscrap,thescrapvariancesarevaluatedatstandardcost.Iftheappropriateindicatorissetinthevariancecategoryofrelevanttargetcostversion,thescrapvariancesaresubtractedfromtheactualcoststocalculatethetotalvariancesandtheproductionvariances.controlcostsControlcostsforvariancecalculationWhenvariancesarecalculatedontheinputside,thecontrolcostsareparedagainstthetargetcosts.InOverheadCostControlling,thecontrolcostequalstheactualcost.

InCostObjectControlling,thisfieldshowseithertheactualcostfromwhichtheworkinprocessandscrapwasdeducted,orthecostcalculatedinpreliminaryordercosting(whichmaybeperiod-based).Whichcostisshowndependsonthetargetcostversion.

Inthefirstcase,thecontrolcostiscalculatedwiththefollowingformula:

Controlcost=ActualcostminusScrapminusWorkinprocessTargetcosts.Toenabletheplannedcostsorthestandardcoststobeparedwiththeactualcosts,itisnecessarytohaveamonbasisofparison.IntheOverheadCostControllingponent,thebasisofparisonistheactualactivityquantity.Theplannedcostsareadjustedtotheactualcosts(whichisanotherwayofsayingthatthetargetcostsarecalculated)usingtheoperatingrate.

InCostObjectControlling,thebasisofparisonisthefollowing:

Forplanningvariances(SAPstandardtargetcostversion2),thebasisofparisonistheplannedorderquantity.

Forproductionvariances(targetcostversion1and3)andthetotalvariance(targetcostversion0),thebasisofparisonistheyield.

Use

InOverheadCostControlling,targetcostsarecalculatedbymeansoftargetcostformulas,onthebasisoftheoriginalcostelements.InCostObjectControlling,thecalculationofthetargetcostsiscontrolledbythetargetcostversion.Thetargetcostforeachmaterialiscalculatedasfollows:Coststhatvarywiththelotsizearedividedbythecostinglotsizeandmultipliedbythecontrolquantity.

Coststhatdonotvarywiththelotsize(suchassetupcosts)aretreatedastargetcostsdirectly.

DependenciesThesetargetcostscanbeusedinCostObjectControllingforthefollowingpurposes:Invariancecalculation

Inthedetaillistinvariancecalculation,thisfieldshowsthefollowinginformation:

Inthecalculationofthevariancecategoriesontheinputside,thefieldshowsthetargetcosts.

Inthecalculationofthevariancecategoriesontheoutputside,thisfieldshowsthetargetcredits.

Inthecalculationofmi*ed-pricevariances,thisfieldshowsthetargetcreditcalculatedonthebasisofthestandardcostsoftheprocurementalternative.

InthedistributionofactualcostsincostobjecthierarchiesThetargetcostscalculatedonthebasisoftargetcostversion0,1or3canbeused.

TargetcostscanalsobeusedtovaluateworkinprocessintheProductCostbyPeriodponent,andtovaluateunplannedscrap(scrapvariances).Thetotalvariancesontheinputsideconsistofthefollowing:Inputpricevariances

Inputquantityvariances

Resource-usagevariances

Scrap(onlyinProductCostControlling)

RemaininginputvariancesInputpricevariancesVariancecategoryontheinputside.

Differencebetweenthetargetcostsandthecontrolcostsresultingfromdifferencesbetweentheplannedpricesandtheactualpricesofthegoodsconsumed.

Use

ThesystemcalculatesandpostsinputpricevariancesforprimarypostingsaccordingtotheentriesmadeinControllingunder"Primarypricevariances."YoucandisplaythisdataintheInformationSystem.

Ifyoucalculatevariancesattheendoftheperiod,thesystemrecalculatesinputpricevariances,providingyouspecifiedquantitiesinadditiontothecostsforthepostings.

Withtarget/actualparisons,thepricevariancesaredefinedbythefollowingformulas:

Inputpricevariance=(Actualprice-Planprice)*Actualinputquantity

Fi*edinputpricevariance=(Fi*edactualprice-Fi*edplanprice)*Actualinputquantity

Variancescausedbybothpricedifferencesandquantitydifferencesareassignedtothecategoryofinputpricevariances.

Ifthequantitiesareinpleteornone*istent,theinputpricevariancesaretakenfromthepostingrecordsastheyhavebeencalculatedfromtheactualcostsforthepostingsasapercentageandactivity-based.Itisnotpossibletocalculateinputpricevariancesifnopercentagerateshavebeendefined.

Theinputpricevariancesareactuallycalculatedwiththefollowingformulas,whichgivethesameresultsastheaboveformulas:

Inputpricevariance=Actualcosts-(Actualinputqty/Targetinput

qty)*Targetcosts

Fi*edinputpricevar.=Fi*edactualcosts-(Actualinputqty"BR>Targetinputqty)*Fi*edtargetcostsInthecaseofactivityinputswithpredistributionoffi*edcosts,thepostedinputpricevariancesofthetotalsrecordsareused.

Withplan/planparisonsofcostobjectsforthecalculationofplanningvariances,theactualdataintheformulasisreplacedbytheplancontroldata.Resource-usagevariancesVariancecategoryontheinputside.Differencebetweenthetargetcostsandthecontrolcostscausedbytheconsumablesandactivitiesbeinguseddifferentlyinthetargetcoststhaninthecontrolcosts.Use

Thevariancecalculationprocessdeterminestheresource-usagevariancesbyperiodforeachcostelement.Resource-usagevariancesarecalculatedifeithernocontrolcostsornotargetcostse*istforacostelement,acostcenter(activityordistribution),anorigingroup,amaterial,andtheplantforthematerial.Withtarget/actualparisons,resource-usagevariancesaredefinedbythefollowingformulas:Resource-usagevariance=Actualcosts-Targetcosts-Inputpricevariance

Fi*edresource-usagevariance=Fi*edactualcosts-Fi*edtargetcosts

-Fi*edinputpricevarianceWithplan/planparisonsofcostobjectstocalculateplanningvariances,theactualcostsintheformulasarereplacedwiththeplancontrolcosts.Dependencies

Origingroup,material,andplantonlye*istinCostObjectControlling.E*amplesSupposeyourfinishedproductFIN*usesrawmaterialRAWA.ThestandardcostestimateforFIN*includesthecostofRAWA.Whenyouproducethematerial,RAWAturnsouttobefaulty.YoudecidetouseRAWBinstead.TheuseofRAWB,however,resultsinhighercoststhanwouldhavebeenthecasewithRAWA.ThedifferencebetweenthecostsplannedforRAWAandthecostsincurredbyRAWBarereportedbythesystemasaresource-usagevariance.Scrap(onlyinProductCostControlling)Scrapvariancesarecalculatedinthevariancecalculationprocess.Dependencies

ScrapvariancesarevaluatedaccordingtothestrategyspecifiedinCustomizingforCostObjectControllinginthevaluationvariantforworkinprocess(targetcosts)andscrap.Ifyouhavenotdefinedavaluationvariantforscrap,thescrapvariancesarevaluatedatstandardcost.Iftheappropriateindicatorissetinthevariancecategoryofrelevanttargetcostversion,thescrapvariancesaresubtractedfromtheactualcoststocalculatethetotalvariancesandtheproductionvariances.RemaininginputvariancesVariancecategoryontheinputsideDifferencebetweentargetcostsandcontrolcoststhatcannotbeassignedtooneofthefollowingcategories:Inputpricevariance

Inputquantityvariance

Resource-usagevariance

Use

Thevariancecalculationprocesscalculatestheremaininginputvariancesbyperiodandcostelement.DependenciesIfyouspecifiedinthevariancevariantthatyoudonotwanttocalculateinputpricevariances,inputquantityvariances,orresource-usagevariances,thesystemwillonlycalculateremaininginputvariances.E*amplesSupposethatinCostObjectControllingmorematerialswerewithdrawnfromstockforaproductionorderthanwereplanned.Inaddition,moreactivitieswerechargedtotheorderthanwereplanned.Thismeansthattheactualinputquantitiesforthematerialsandactivitiesactuallyconsumeddifferfromthetargetinputquantities.Thissituationwillresultinanincreaseinthecalculatedoverheadratesbecausetheinputquantityvarianceincreasedthebasisforoverheadcalculation.Thevariancesthatarisefromthedifferencebetweentheplannedoverheadrateandtheactualoverheadrateduetothechangedbasisareassignedtothecategoryofremaininginputvariances.outputsidevariances:Fi*ed-costvariances(OverheadCostControllingonly)

Lotsizevariances(ProductCostControllingonly)

Outputpricevariances

Outputquantityvariances(OverheadCostControllingonly)

RemainingvariancesFi*ed-costvariances(OverheadCostControllingonly)VariancecategoryontheoutputsideFi*edcostvariancesoccurwhenaportionofthefi*edplancostsisnotcoveredby,orisoverabsorbedby,thecreditswhentheactualoperatinglevelisnotthesameastheplanoperatinglevel.Fi*ed-costvariancesconsistofthevolumevarianceandthesecondaryfi*ed-costvariance.Use

Variancecalculationdeterminesthefi*edcostvariancesperiodically.Procedure

Fi*ed-costvariancesresultwhentheoperatingrateisnot100%.Fi*ed-costvariancesaredefinedbythefollowingformula:Fi*ed-costvariance=Fi*edplancosts*(1-operatingrate)

+Fi*edtargetcosts-fi*edplancostsInmanycasesthefi*edtargetcostsareequaltothefi*edplancosts.Ininternalactivityallocation,however,thiscanresultinadifferencebetweenfi*edplancostsandthefi*edtargetcosts(seetargetcostformula4).Thisdifferenceismarkedasavarianceinthefi*edcostvariances.Thefi*ed-costvariancesareactuallycalculatedwiththefollowingformula,whichgivesthesameresultastheformulaabove:Fi*ed-costvariance=Fi*edtargetcosts

-Fi*edplancosts*(actualqty/planqty)Lotsizevariances(ProductCostControllingonly)Variancecategoryontheoutputside.Differencebetweenthelot-size-independentplancostsandthelot-size-independentchargedactualcosts.Lot-sizevariancesoccurwhenaportionofthetotalcostsforanorderdoesnotchangewhenthequantityofgoodsmanufacturedischanged.Use

Variancecalculationdetermineslot-sizevariancesbyperiod.Procedure

Lot-sizevariancesarecalculatedwhentheplanquantity(theplanorderquantityorthelotsizeofthestandardcostestimate)differsfromtheactuallyproducedquantityorcontrolquantity.Withtarget/actualparisons,thelot-sizevariancesarecalculatedwiththefollowingformulas:Lot-sizevariance=

Lot-size-independenttargetcosts*(1-actualqty/planqty)Fi*edlot-sizevariance=

Fi*edlot-size-independenttargetcosts*(1-actualqty/planqty)Withplan/planparisonsofcostobjects,theactualcostsintheformulasarereplacedbytheplannedcontrolcosts.OutputpricevariancesVariancecategoryontheoutputside.Differencebetweenthetargetcreditandtheallocatedactualcosts.InOverheadCostControlling,anoutputpricevarianceresultsfromtheuseofanallocationpricethatdoesnotcreditthecostcenterwiththetargetcosts(thatis,iftheplannedactivitypriceisdifferentfromthepricewithwhichtheactivityisvaluatedininternalactivityallocation).Thiscanbethecasefore*ampleifyouvaluatetheinternalactivitieswithpoliticalprices,usethecapacityasthebasisforplannedpriceiteration,oruseaverageactivitypricesinsteadofperiod-basedprices.InProductCostControlling,anoutputpricevarianceresultswhentheactualcreditofanorder(suchasaproductcostcollectororproductionorder)doesnotequalthetargetcredit.ThisisthecasefordeliverytostockforamaterialwithpricecontrolindicatorVatapricethatisnotthestandardprice.Theactualcreditiscalculatedasfollows:InOverheadCostControlling,theactualactivityisvaluatedwithanallocationprice.

InProductCostControlling,thedeliveredquantityortheorderplanquantityisvaluatedwithapricefromthematerialmasterrecord.Thevaluationvariantforthevaluationofgoodsreceiveddetermineswhetherthegoodsreceiptisvaluatedwiththestandardprice,themovingaverageprice,oraplannedprice.

Thetargetcreditiscalculatedasfollows:InOverheadCostControlling,thefi*edandvariableplannedcostsaremultipliedbytheoperatingrateofthecostcenter/activityorprocess.

InProductCostControlling,thedeliveredquantityortheorderplanquantityisvaluatedusingthestandardpriceforthematerialproduced.

Iftheobjectisasenderinthepredistributionoffi*edcosts,thefi*edtargetcreditdoesnotdependontheoperatingratebutisequaltothefi*edplannedcosts.Iftheactualquantityfortheobjectisenteredmanually(thisisnotpossiblewithallCOobjects),theoutputpricevarianceiscalculatedinthesamewayastheinputpricevariance:Outputpricevariance=Targetcredit*(Manualactualqty"BR>Allocatedquantity)-Allocatedactualcosts

Fi*edoutputpricevar.=Fi*edtargetcredit*(Manualactualqty"Allocatedqty)-Alloc.fi*edactualcostsUse

Variancecalculationdeterminestheoutputpricevariancesbyperiod.Outputquantityvariances(OverheadCostControllingonly)Variancecategoryontheoutputside.Differencebetweentheactualcreditandthetargetcreditduetodifferencesbetweentheallocatedandthemanuallypostedactualquantities.Use

Variancecalculationcalculatestheoutputquantityvariancesbyperiodandcostelement.Procedure

Theoutputquantityvarianceisdefinedbythefollowingformulas:Outputquantityvariance=(Actualqty-Manualactualqty)*

Actualactivityprice

Fi*edoutputqtyvariance=(Actualqty-Manualactualqty)*

Fi*edactualactivitypriceVariancesthatareduetobothoutputpricedifferencesandoutputquantitydifferencesarenotassignedtotheoutputquantityvariancesbutarereportedinsteadasoutputpricevariances.Iftheactivityparticipatesinthepredistributionoffi*edcosts,thefi*edtargetcreditisnotproportionaltotheoperatingrate.RemainingvariancesVariancecategoryontheoutputsideshowingthedifferencebetweenthetargetcostsandtheallocatedactualcoststhatcannotbeassignedtooneofthefollowingvariancecategories:Mi*ed-pricevariance(onlyinProductCostControlling)

Outputpricevariance

Outputquantityvariance(onlyinOverheadCostControlling)

Lotsizevariance(onlyinProductCostControlling)

Fi*edcostvariance(onlyinOverheadCostControlling)

Remainingvariancesarenotlistedbycostelement,butbyControllingobject.TheR/3Systemcalculatesthevariancebytakingthetotalvarianceandsubtractingallothervariancecategories.Use

Variancecalculationcalculatesremainingvariancesbyperiod.Dependencies

Thefollowinge*ceptionsarepossible:Minordifferencescangointothecategoryofremainingvariances.

Ifonlytheremainingvariancescategoryisactive,theremainingvarianceisthedifferencebetweenactualcostsandallocatedactualcosts.Allvariancecategoriesappeartogetherasaremainingvariance.

IftherearenotargetcostsfortheControllingobject,allvariancecategorieslikewiseappearasaremainingvariance.Thiswillbethecase,fore*ample,ifvariancecalculationcannotselectanactivestandardcostestimateforthematerialproduced.ActualcostallocationsSpecifiesthecostswithwhichtheobjectiscredited.Whenthevariancesarecalculated,thesecostsareparedwiththetargetcoststocalculatethevariancecategoriesontheoutputside.InOverheadCostControlling,thesecostsaretheactualcreditsfromactivityallocations.

InCostObjectControlling,thesecostsincludetheactualcreditsfromdeliveriestostock.CalculationAccuracyThecostsarecalculatedusingthesamenumberofdecimalplacesasthecurrencyinwhichthecostsarerecorded.Inmostcurrenciesthisistwodecimalplaces.Quantitiesarecalculatedusingthesamenumberofdecimalplacesastheunitofmeasureinwhichtheyarerecorded,uptoama*imumofthreeplaces.Quotientsofquantities(suchasactualquantity"targetquantity)arecalculatedusingsi*decimalplaces.Aftereachputationstep,thecostsandquan