Hello I need help if you can with inputting and calculating meter readings. This would help cut down on multiple inputs manually. Any help would be greatly appreciated. Here is what I do.

I read several different meters on different days and subtract new readings from previous and average between the days. These days are not consistent so I manually subtract readings and divide by number of days. Sorry if this is confusing maybe this will help.
MeterA Usage MeterB Usage MeterC Usage
Day1 0 0 877654 0 432 432
Day2 76543 76543 617 111.2
Day3 883.25 878888 617 111.2
Day4 883.25 10893.5 111.2
Day5 883.25 900675 10893.5 111.2
Day6 80076 883.25 988 111.2