on-time-delivery performance measurement

Hi ,

In standard SAP, the on-time delivery performance is measured based on the statistical delivery date and the GR posting date.

I want to measure the On-time-delivery performance based on the delivery date in the PO and not based on statistical delivery date.

So it is possible to do that? If yes, how?

If no , Is there any user exit where we can write a code that if some body changes the delivery date in PO, using ME22N, the statistical delivery date should also be updated same as changed delivery date?

Please help.

Thanks in advance.