Get a daily use average?

[tl7612]

I have a monthly spreadsheet that numbers are keyed in from readings that are done on different days of the month. The spreadsheet has the dates in across the top in row 1 and the locations in the rows below. For example, I would have a reading on April 8th for 83,055,000 and then on April 15th for 83,203,000. I of course could do the the math and get the daily average between those two numbers by substracting the two and divide by 7. That would get me a daily average use of 21,143. However, I will have more dates keyed in and would like a formula to figure out what the daily average use would be no matter what dates entered.

 

[Joe4]

For example in April there are 30 days and the formula divides by 29 days instead of 30 days. There would always be a reading on the first day of the month and the last day.

As it should if you are really trying to get daily usage. From April 1 to April 30 is 29 days. 30 days from April 1 would by May 1, not April 30.

This is more easily see with the following simple example.
Let's say that you are comparing 2 readings, one from April 1 and one from April 2.
That is one days change. If you divide by 2 (i.e. 2-1+1), you are going to get half of the actual daily usage, not the full amount (as there is really only one day difference, not two!).