Use excel to show long term sales increase

I have a spreadsheet which is around 16,000 rows long which helps me to decide what items i need to re order. I want to be able to identify products which have increased by over 25% in volume so we can negotiate prices with suppliers. I use a simple formula to compare sales average from Jun-Mar with sales from May-Feb which identifies a sudden spike, but i also want to see if there is a gradual increase. Any ideas? Cumulative % maybe? Im lost, the zeros dont help when i try to calculate a cumulative % changes......



4 month average Jun May Apr Mar Feb Jan Dec Nov Oct Sep Aug Jul
7 20 0 8 0 2 1 0 0 0 8 1 0
2 5 0 0 4 0 0 0 0 0 4 1 0
16 0 0 6 9 50 0 12 5 0 8 0 0
1 1 0 1 0 1 4 4 0 0 4 0 0
1 0 0 0 2 0 0 0 0 0 2 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0

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