How to measure "OTD" for EX-Work Shipments?

s an On Time Delivery OTD metric taken on any given date measured by what has shipped on that date only (whether the shippments were late or on time) ? i.e. Shipped 10 orders on a date. Of those 10 orders, 1 was late and 9 were on time - 90% OTD or Is an On Time Delivery OTD metric taken on any given date measured by what has shipped on that date vs. what was due on that date ? i.e. 10 Orders were shipped on a date, 1 of those was late, however, 10 other orders were also due but not shipped - 45% OTD