Coding Mask for the Appropriation Request Number 
Use
You can keep your appropriation request numbers more uniform by using coding masks. These coding masks assist in the formatting of character strings. The procedure and the coding masks are the same as those used for formatting WBS element keys in the Project System (PS) component.
In order to use coding masks, you have to set the indicator for Same external coding mask and number assignment as WBS element in the appropriation request type. Setting this indicator has the following results:
It is not possible to format the appropriation request number independently of the resulting WBS elements. Using coding masks is also not possible if the measures created later are internal orders.
Features
Coding Mask for the Appropriation Request Number
The system uses the coding mask ID and the leading characters of the appropriation request number to determine the coding mask to be used. If these two agree, the system tries to apply the coding mask to the appropriation request number entered. If this does not work, the system issues an error message. Using coding masks helps to ensure that the keys of your appropriation requests all have a certain structure.

Coding Mask for the Appropriation Request Number
You also specify in Customizing which special symbols are allowed in the coding mask. The system sets the special symbols in the coding mask automatically, if the first characters of the character string you enter agree with the coding mask ID: The functions of other indicators for the coding mask include:
Restricting the Coding Mask
You can assign coding masks to appropriation request types for the formatting of the appropriation request number. In addition, you can specify a slightly different coding mask, which the system should then use for the numbers of projects/WBS elements that are created from these appropriation requests.
Activities
You maintain all settings for coding masks in Customizing for Investment Management. Choose Appropriation Requests ® Master Data.
For more information, see:
Coding Mask for the Appropriation Request Number
Specify Special Symbols for Approp. Request Number
Define Coding Mask for the Appropriation Request Number