Oracle Internet Expenses Mileage Rate

Hi,

We have defined Policy Schedule for Mileage. We have a requirement where we need to enter expense line for each day and need to calculate average distance  for all the lines which are entered within that expense report. Depending on the average distance for all the lines we need to override the rate which is calculated from Policy Schedule for all the lines. How can we acheive this. Please advise.

Thanks,
Vijaya