How to calculate a Global change of the difference between two date fields in calendar days?

I want to see the Total Float for all activities in calendar days, i.e., elapsed days on a 7-days-a-week/no-holiday/no-weather-day basis, without reference to the task calendar.  I set up a new number field and a Global Change to calculate the difference between the Early and Late Finish dates.  The result was based on the task calendar.  How do I normalize the result to be elapsed/calendar days?