An allocation source identifies the account, or range of accounts, to be used as the basis for an allocation. Selected transactions posted to these accounts provide the source amount to be manipulated and allocated.
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An allocation source is created and maintained using Corporate Allocation Source (ALS). Each allocation source is identified by a unique allocation source code. This code is then referenced on an allocation sequence, in Allocation Setup (CALS).
Allocation sources are described in more detail in What are Allocation Sources?

Allocation Source Code
The code that uniquely identifies the allocation source.
Allocation Source Continuation
A continuation indicator is used to specify additional account ranges and analysis selection criteria, if they are required to select the appropriate source account transactions. You must leave this field blank on the first record of an Allocation Source.
The Offset account, Source Amount, Ledger Code and Threshold fields are ignored on an Allocation Source Continuation. This information is only provided on the first allocation source record and applies to all of the continuation records.
Allocation Source Name
A descriptive name to identify the allocation source.