Parameter 1 is the custom field name of type date of the Custom Purchase Date.

Parameter 2 is the custom field name of type date of the Custom Install Date.

This rule copies standard fields, Purchase Date and Installation Date, into custom fields as defined in the parameters.

For example, if your custom purchase date field is named Date Purchase, like Parameter 1, the value will be copied to the standard Purchase Date field when the standard field is null. If the standard purchase date field has a value and the custom field does not, the standard field value will be copied into the custom purchase date field from Parameter 1.