Having issues with nested formulas

[snm6996]

I have a spreadsheet to determine the number of hours a machine worked from one month to the next based on meter readings. However, if a meter reading wasn't entered for a month (total of zero), I need the formula to go back each month until it finds a month where the meter reading is greater than zero.
My spreadsheet is for a year, so there is a possible 12 ifs for the formula to go through.

This is my formula for April and I need it to go to December (cell DV3)​

=(IF(AND(AS3=0),0,IF(AND(AI3>0),AS3-AI3,IF(AND(AI3=0),IF(AND(AI3>0),AS3-Y3,AS3-U3))))))
What is the best way to do this?

 

[sandy666]

you forgot about condition

=IF(AS3=0,0,IF(AI3>0,AS3-AI3,IF(AI3=0,[B][COLOR="#FF0000"]???[/COLOR][/B],IF(AI3>0,AS3-Y3,AS3-U3))))

and it looks much simpler without AND()

for the rest I do not know what you want to achieve (maybe someone else)
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