Hi. I run a small water utility company.  I am in the process of converting my flat Excel records into an Access Database.  The learning curve is steep.  I have started Rick's classes, but I'm trying to figure out how calculate a client's bill.  I've figured out A way to get the balance forward, and previous meter readings, but I have two issues that are defeating me.  First, my clients each have a per unit rate that can change based on whether or  not they've paid their full connection fee.  So, I've been storing the unit rate in each record. I know that is unnecessary duplication, but I can't figure out how to keep my system from recalculating their entire billing history if I change their rate unless I do.  So that is issue one.  My second issue is that we occasionally bill an average or estimated bill when a client's meter is faulty.  I need to be able to calculate the rolling 12 month average bill and choose that instead of the calculated bill (units used*rate). I'm absolutely certain Rick covers this in a class, seminar, or tech help video, but I haven't yet found a tech video that addresses these two issues and I'm not far enough in the classes to figure it out on my own.   Thanks for your help.