Formula Parameter 
Formula Parameter
A formula is identified by its formula key. It is composed of formula parameters that are identified by parameter IDs.
You create formula parameters and formulas in Customizing for work centers:
You assign each formula parameter to a data field in the work center or routing. When the formula is evaluated, each formula parameter has the value that you have entered in the corresponding data field.
The Origin of Formula Parameter Values
You must enter the origin of every formula parameter in Customizing. The origin controls the assignment of formula parameters to data fields. According to its origin a formula parameter is either automatically assigned to a data field or you have to enter a field name as well as the origin.
You can refer to formula parameters in work centers or routings either by the parameter ID or by the key word, which you have to assign to every formula parameter in Customizing. This key word appears with the assigned field in the work center or routings screen.
Formula parameter values can have the following origins:
With the help of the standard value key you can assign up to six formula parameters for standard values to a work center and consequently to an operation in a routing.
You can assign a constant value and a unit to up to six work center constants.
You assign general formula constants a fixed value and an unit in Customizing for Formula parameters
The formula parameter is linked to a data field in the general operation data. Typical fields are:
If formula parameters have this origin, you must enter the corresponding field names in Customizing.
The value of a user-defined field in the operation is assigned to the formula parameter.
In this case the user-field key also controls the assignment of the formula parameter to the data field by making two data fields available for formula parameters. You define user-field keys in Customizing Routings under Create user-defined fields The key words, with which the data fields are labeled in the operation, are not defined in the formula parameter directly, but in the user-field key.
You assign a data field in the production resource/tool assignment to the formula parameter, for example:
You assign constant values to the formula parameters in the PRT master record.
These formula parameters can only be used in formulas for PRT management.