I have a table that shows monthly production volumes for circa 2 years up to Oct 2016. However, there are months where there is zero production because of shutdown etc. I need a formula that sums 12 months backward rolling production from Oct 16, ignoring the zeros. I.e, if you look at the table below Aug 15 to Oct 16 is 15 months, but because 3 months have zero production, its actually 12 months of production. The file has many of such rows, with the zero production months popping up in different months.

is there a simple formula that would work for all the rows and only add 12 months of production, ignoring the zeros?

Please help. Would be very grateful for any solution to this.

Aug-15 | Sep-15 | Oct-15 | Nov-15 | Dec-15 | Jan-16 | Feb-16 | Mar-16 | Apr-16 | May-16 | Jun-16 | Jul-16 | Aug-16 | Sep-16 | Oct-16 |

84,890 | 91,260 | 90,560 | 80,969 | - | - | 91,941 | 111,089 | - | 85,835 | 26,698 | 7,637 | 67,308 | 72,185 | 521 |

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