A deferred parameter is a process input value that is passed up one recipe level. By deferring a parameter, you instruct a recipe to retrieve the parameter's value from a formula. By creating a chain of parameters, you input the desired values at a high level (typically the procedure level) and pass the values all the way down to the phase. This approach lets you use generic operations that are shared by multiple recipes.
For the paint application, we want to be able to vary the values for three phase-level batch input parameters by creating formulas at the procedure level. The parameters we want to vary are as follows:
To be able to specify the values for these parameters at the procedure level, we need to create equivalent parameters at the lower recipe levels (operation, and unit procedure) and defer them up to the top level.
We will start by creating an operation level parameter for the amount of base to be charged. The lowest recipe level at which this parameter is used is OP_CHARGE. (OP_CHARGE contains the phases CHG_BASE as well as CHG_COLOR.)