通过实务简单讲，sap把收货和发票校验入帐拆分给了两个部门，收货动作就是GR,是由仓库做的存货入帐动作，借存货，贷过渡科目，当收到发票时，财务部门做发票校验入帐动作，借过渡科目，贷应付账款，这样借贷方的过渡就清掉了。
但是由于过渡科目是个虚科目，月末不能在帐上留余额，所以如果当月仓库收货了，而我们没收到发票，那么月末就需要运行暂估程序，把留在系统中的过渡贷方余额转入一个实科目，叫应付账款-暂估，这样我们的试算表就平了；
到了下个月由于这批货物的发票到了需要入帐，系统会借一个过渡科目，但是由于上月底我们把收货的贷方过渡转到了应付账款暂估，没办法对过渡进行清账，所以系统设置了暂估程序次月自动回冲的功能，即当月末把贷方收货过渡转入贷方应付账款暂估后，在次月系统又会将这笔分录自动回冲，使得收货过渡依然留在过渡科目贷方，等待与发票入账产生的借方进行清账。
以下为专业解释
GR/IR is to perform the three-way match – purchase order, material receipt, and vendor invoice. You use a clearing account to record the offset of the goods receipt (GR) and invoice receipt (IR) postings. Once fully processed, the postings in the clearing account balance.
Clearing is performed at the purchase order (PO) line item level based on quantity entered. Price variance and exchange rate variance are calculated. You can write off small differences using transaction MR11.
Purchase Price Variance
This discussion assumes you are using standard price control (S) for purchased materials. The quantity and amount on the GR and IR postings are important. You must have posted GR to record purchase price variance (PPV). There is no PPV posting for just IR. There can be additional variance postings on IR after GR is posted for differences between PO price and actual price paid.
When posting GR, the price variance is based on the PO price, unless IR has already been posted, then it is based on actual price paid. If IR has already been posted, the GR will be based on the IR up to the quantity of the IR, after that is will use the PO price again.
After all postings to a PO line item, the net PPV posted will be the difference between the actual price paid and the standard cost of the material.
General Ledger Account Determination
G/L Accounts are defined with MM Account Determination IMG Transaction OBYC / Table T030.
Attributes include Valuation Class, as defined in the material master Accounting 1 view.
GR/IR accounts are defined with Transaction WRX.
Price Variance Accounts are defined with Transaction PRD.
Month-end Restatement
You restate balances in these G/L accounts as inventory or payables at month end with transaction F.19. The accounts are defined in table T030U and set with configuration transaction OBYP.
Debit balances T030U transaction BNG - Invoiced not yet delivered map to Inventory G/L Accounts
Credit balances T030U transaction GNB - Delivered not yet invoiced map to Payable G/L Accounts
Exchange Rate Variance
For materials purchased in a foreign currency, you can map variance due to exchange rate difference to a different G/L account with configuration in IMG menu path: Material Management > Logistic Invoice Verification > Incoming Invoice > Configure How Exchange Rate Differences are Treated.
You can map variance due to exchange rate change to separate G/L accounts with MM Account Determination Transaction KDM.
You can choose from several options to control how exchange rate differences are handled for invoices in foreign currencies. One of these calculates the exchange rate variance as the difference between the current exchange rate at the time of invoice processing and the plan exchange rate for the year.
Tools/Reports for GR/IR and PPV
The following transactions are available for GR/IR processing and reporting:
FBL3N G/L Account Line Item Display
ME23N Display PO (PO History tab, suggest using of Chronological Order function)
MR11 GR/IR Account Maintenance
MB5S List of GR/IR Balances
FS10N G/L Account Balance Display
F.13 Automatic Clearing (clear on PO/item combination)
F.19 Analyze GR/IR Account and Accrual
MR11SHOW Display/Reverse MR11 document
CKM3N – Material Price Analysis
KKML0 – Material Ledger Drilldown Reporting
