for user growth do we need formula

output i got for user growth for product per week here i have calculated use of product per week. if its not correct can u pls explain what is user growth in detail.... device usercount weeknum macbook pro 57295 18 lenovo thinkpad 36978 18 macbook air 26786 18 iphone 5 25883 17 dell inspiron notebook 19669 17 samsung galaxy s4 18653 18 nexus 5 16502 17 iphone 5s 15929 19 ebook 8930 19 hp pavilion desktop 8881 17 nexus 7 6540 18 nokia lumia 635 5612 17 ipad mini 5591 18 acer aspire desktop 5173 17 nexus 10 5139 18