m₁ / m₂
with:
m₁ = Distinct Count([Order Items].[Order Eid])
    WHERE
        [Order Items].[Order Completed Date] ≥ 'Start of Current Period'
        AND [Order Items].[Order Completed Date] ≤ 'End of Current Period'
        AND [Order Items].[Is 0 Dollar Order] = false
m₂ = Distinct Count([Order Items].[Order Eid])
    WHERE
        [Order Items].[Order Completed Date] ≥ 'Start of Current Period'
        AND [Order Items].[Order Completed Date] ≤ 'End of Current Period'
        AND [Order Items].[Is 0 Dollar Order] = false