Average Daily Sales calculation with multiple operating day schedules

I'm struggling to find a solution to calculate the daily sales average which is sales divided by the number of operating days. This makes a comparable values between partial and complete months.

Each operating day has thousands of records. The problem I'm running into is calculating the correct denominator. I have the schedule pulled into Tableau with True/False listing the non-operating days.

Each operating day has hundreds of records so a formula like below produces an insane value.

{FIXED : COUNTD(IF [Operating Day = True] THEN [Ship Date] END)}