It might need a kind of visual explanation how this metrics is calculated and all the rest is pure math.
There are 60 rows showing well known 60 days period.
There are columns where T means today, T+1 means tomorrow, T+2 day after tomorrow etc.
The numbers inside the matrix show the orders.
1 means 1 order completed on time, 0 means 1 order not completed on time…
Delivery on Time (%) is calculated as sum of 60 rows / divided by count of the orders of 60 rows.
As time changes the Delivery on Time metrics changes.
In this example I would be at 67% today, in 3 days i would be at 71% because I would deliver new order on time, on day T+11 I would be at 83% because one order that was not delivered on time has gone from calculation (resp. from 60 days period) etc…
It would be a big surprise on day T+52 because of drop to 67% but even bigger surprise on day T+53 when I would be at 100% again. Huray! (P.S. many users would likely consider it as a bug or something, saying something is wrong, I do not understand,… but we know that it works exactly how it is supposed to work )