1. The checking group + checking rule determine how the availability check is to be performed.

2. The checking group determines whether and how the system checks the stock availability and generates requirements for material planning. The checking group defines what type of requirements will be passed on i.e. summarized requirements (daily/weekly) or individual requirements for each sales order.

3. The checking rule applies to how the availability check is to be carried out at the transaction level. Note that you must define checking rules for each individual application such as for production orders for example. In Sales and Distribution, the checking rule is specified internally within the system and cannot be changed.

4. The checking rule, in conjunction with the checking group, determines the scope of the availability check for every business operation; that is, which stocks, receipts and issues are to be included in the availability check and whether the check is to be carried out with or without the replenishment lead time.

5. Briefly explaining the above – checking group determines which type of requirement to be passed on to MRP whether it be individual or summarized and checking rule which is at the transaction level and can be configured independently for each application module, determines which stocks, receipts and issues to be taken into account. For performing an availability check checking group has to work in conjunction with checking rule.

6. Advantages of individual processing over summarized processing – 
Backorder processing is possible.
You can access (MD04) order, line and schedule line individually which gives a greater control on available stock and requirements placed on stock.
The system automatically uses individual requirements in case of special stock items.

7. Required data for the Availability check to be carried out –
The Availability check must be switched on at the requirement class level.
The Availability check must be set at the schedule line level.
A requirements type must exist by which the requirements class can be found.
A plant must be defined in the sales order for each schedule line item (in other words plant must be defined for every material in MMR).
A checking group must be defined in the material master record in the MRP3 screen in the availability check field.

8. Configuring Availability check and defining Checking Groups –
Checking groups are introduced into the sales order based on the setting in the material master record.
SAP standard checking groups are 01 – summarized requirements and 02 – individual requirements or you can create your own by copying the standard ones.
Total sales and total deliveries columns are there to configure a checking rule to sum up requirements to post to MRP either individually or by day or week.
Block quantity required can be set if you want several users to be able to process the material simultaneously in different transactions without blocking each other.
The no check indicator is CHECKED when you DO NOT want the system to carry out ATP check.

9. Defining material block for other users – the block check box is an indicator that enables you to block material master records of a particular material during the availability check and restrict other users from accessing same master record and reserve the material. If the block is not set, two users can confirm the same material at the same time for two different orders, not knowing if the stock is available or not. If you select this field, the material is blocked during the availability check and other users cannot: a) Make changes in the material master record. b) Create purchase orders for the material. C) Create orders for the material.

10. Defining default values for checking groups - Checking groups are introduced into the sales order based on the setting in the material master record.
However if there is no entry present in the material master record for the checking group, a default value can be set here, depending on material type and plant.
This default value will be used by the system depending on the material type mentioned in MMR and plant in sales order.
If an entry exists, this default value is over written by MMR.

11. Controlling Availability Check – in this section, you tell the system what stock on hand and what inward and outward movements of stock it must take into account when performing the availability check in addition to whether or not to consider the replenishment lead time.

12. These settings are based on the checking group that is assigned to the material master record and the checking rule that is predefined and assigned to the sales and distribution transaction.

13. These settings carry out control both for sales order and delivery as well. This is due to the fact that you may want to include specific stock or incoming stock for the sales order, yet at the time of the delivery only include physical stock on hand waiting to be shipped.

14. It is possible to indicate to the system that you would like the availability check NOT TO CHECK the stock at the storage location level. This indicator is used to set the scope of the availability check. 

15. It is used to switch off the check at storage location level. You create a reservation for a particular storage location. However, the scope of the availability check is set in such a way as to exclude the storage location. In this case, the system carries out the check at plant level only and does not take the storage location into account that is specified in the reservation.

16. Should you not want the system to automatically check RLT, you may indicate so here. RLT is the time taken for a material to become available. It is only used when doing an ATP check and is taken from MMR.

17. Defining the elements in the availability check entirely depends on the business needs, but a few tips are given under – 
When controlling the Availability check at the time of the sales order, a purchase requisition does not necessarily indicate by it is going to come into the plant.
A shipping notification on the other hand - a confirmed purchase order – is a good indicator of receiving stock on a specified date.
It is always recommended not to select the shipping notifications for the delivery requirements type as you may not actually receive the stock into plant or warehouse for which you are creating a delivery.

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