Multiple Report Parameters with expression

[Chuck Harrington]

I am trying to set up multiple parameters for a report.  The first has a datasource that lists a series of dates from a table.  This is no problem. What I want to do is calculate an 'end date' value for the second parameter based on the date selected in the first parameter and then pass the two parameters to the SQL statement that is the datasource for the report.  I know how to accomplish the second part and have written the calculation procedure I need in a class module.  What I can't figure out is how to invoke the procedure when the user selects a date in the first parameter. Thanks for any suggestions