How to calculate r squared

[Kamarlon]

I have monthly data which I am trying to analyse in a dashboard. One idea I have is to give users options to add a linear trend line to a graph I created. However i want to write a statement stating whether the data follows a linear trend or not. I know how to write the statement, what I don't know is which formula is best to calculate teh r squared valued.If the r squared value is high I plan on showing teh sentence : "Revenue from May 2009 to June 2011 follows a linear trend", otehrwise it will say it does not.

 

[OleMiss2010]

Excel has an R Squared formula:

=rsq(known y's, known x's)

 

[Kamarlon]

Yep that did teh trick. Thank you very much. I searcehd the list of formulas and some how did not see rsq...go figure. It may seem strange taht I want to add a trend line option and then tell users whether it follows a trend or not, but persons tend to report graphs with linear trend line even when its not teh best fit. Thanks again