growth type/distribution formula

[Jul2010]

I have some monthly historical sales data and would need to do a forecast for
next 12 month.
Question - sales number - how can identify the closest rule on their growth
or change? Is there a way to accurately identify the growth type - linear or
exponential or any any other?

 

[Gary''s Student]

Plot the data. See if a linear fit is "good enough". Then try some sample
fits:

http://spreadsheetpage.com/index.php/tip/chart_trendline_formulas/