During an update, the system:

• Reads posted count results that have been added
• Determines changed book inventory balances and book values
• Determines whether subsequent random selection is required

In inventory sampling, any count entered or difference posted is recorded in the relevant physical inventory document. However, this information is not updated automatically in the inventory sampling concerned. This will only be done during the update process.

During the update, the system checks the physical inventory documents created for inventory sampling and uses any required information from these documents for extrapolation.

The value of stock management units that have already been counted, and for which differences have been posted, are no longer updated; the inventory differences that occur are extrapolated in the current sampling stratum. This prevents stratum changers resulting from current goods movements after the inventory differences are posted. In Customizing for Inventory Management, you can define whether counted and posted stock management units are to be updated by choosing Physical Inventory -> Inventory Sampling -> Create Physical Inventory Profiles and the Update counted and posted stock management units indicator.

In inventory sampling, the system differentiates between three points in time:

• The time of planning - this is the time when the stock population is formed. The division of the stock population into complete-count area and sampling area, the classification, and the stratification are based on the data at the time of planning.
• The time of physical inventory - this is the time when the physical inventory count is entered and the difference posted.
• The current time - this is the time when the update is carried out. The extrapolation refers to the data at the current time.

If provided for in the physical inventory documents, a posting block for stock management units to be counted only exists in the period between creation of the physical inventory document and entry of the physical inventory count. Before and after this period, inventory postings are allowed. Throughout the inventory sampling, postings can be made without restriction for stock management units that need not be counted. Consequently, changes to the book inventory balances or book values are possible during inventory sampling. This is what is called continuous inventory sampling in the SAP System.

During the update, the system determines these changes and considers them for extrapolation.

The following table shows the stock balance and the value of a stock management unit at different points in time, for example.

During the update, the system determines that the count has been entered and the inventory difference posted for the stock management unit.

To calculate the estimate, which is determined during extrapolation, the system stores the current book value of the stock management unit. In the above example, the current book value is 1776.

To find out to which stratum the stock management unit belongs, the system performs the following calculation: the current book value is increased by the inventory difference of 24. This means that the assignment of the stock management unit to a specific stratum is based on the value 1800. Therefore, the stock management unit may belong to another stratum (see the section below "Determining Whether Subsequent Random Selection Is Required").

In the case of continuous inventory sampling, the book inventory quantities and book values may be changed while the inventory sampling is being carried out. As a result, a stock management unit that belonged to a particular stratum at the time of planning may belong to another stratum at the current time. Stock management units can also be transferred between the sampling area and the complete-count area.

If a stock management unit moves to the complete-count area, it must be counted. The system will then propose a subsequent random selection for the complete-count area.

Switching elements to another stratum can also result in a subsequent random selection: as a result of "stratum changers", the remaining elements that were selected for a stratum may no longer be representative of that stratum. In this case, further elements to be counted must be drawn for this stratum. The system performs this check for each stratum. If it determines that additional elements must be drawn, it proposes a subsequent random selection for the sampling area.

The stratification is based on the data that applied at the time of planning. At the time of the update, the system determines that the materials B and E no longer belong to this stratum. The materials G and H have been added to the stratum. Therefore, the stratum contains 6 elements, of which only one has originally been drawn to be counted. Since this single count does not guarantee that the results for the entire stratum are correct, the system proposes a subsequent random selection. In the subsequent random selection, the system will draw stock management units of the updated stratum that have not yet been counted (the updated stratum includes the elements A, C, F, G, and H).

If, at the time of the update, the system determines that particular stock management units should be contained in the complete-count area due to the current stock values or that a selection made for a stratum is no longer representative, it proposes a subsequent random selection. In a subsequent random selection, the system will:

• Carry out a random selection in the strata for which no representative selection exists, using the elements not yet counted.
• Create a session for generating physical inventory documents for the following stock management units:

• The new stock management units drawn
• The stock management units that have been added to the complete-count area

In each update, you can decide whether or not to carry out the subsequent random selection suggested by the system. If, during the last update, the system recommended a subsequent random selection, you must start the random selection to allow for the final extrapolation.

It is recommended that you do not carry out a subsequent random selection until shortly before the final extrapolation, as during update the system may propose that you carry out a subsequent random selection, though this may no longer be required after the next update has been carried out. For example, this would be the case if goods receipts were posted for various stock management units before an update and corresponding goods issues prior to the next update. If you performed a subsequent random selection as a result of the first update, more stock management units would have to be counted than actually necessary.